Metallurgy & Heat Treatment of Meta
1. Balls for ball bearings are made of
(a) cast iron
(b) mild steel
(c) stainless steel
(d) carbon-chrome steel
Ans: d
2. White cast iron
(a) contains 1.7 to 3.5% carbon in free state and
is obtained by the slow cooling of molten cast iron
(b) is also known as chilled cast iron and is
obtained by cooling rapidly. It is almost unmachinable
(c) is produced by annealing process. It is soft,
tough and easily machined metal
(d) is produced by small additions of magnesium
(or creium) in the ladle. Graphite is in nodular or spheroidal form and is well
dispersed throughout the material
Ans: b
123. Which of the following element results in
presence of free graphite in C.I.
(a) carbon
(b) sulphur
(c) silicon
(d) manganese
(e) phosphorous.
Ans: c
126. Pipes for bicycle frames are made of
(a) cold rolled steel
(b) hot rolled steel
(c) forged steel
(d) cast steel
(e) carbon-chrome steel.
Ans: a
125. Cold rolled steel sheets contain carbon of
the following order
(a) 0.1%
(b) 0.2%
(c) 0.4%
(d) 0.6%
Ans: a
144. The usual composition of a soldering alloy is
(a) tin, lead and small percentage of antimony
(b) tin and lead
(c) tin, lead and silver
(d) tin and copper
Ans: a
145. Admiralty brass used for steam condenser
tubes contains copper and zinc in the following ratio
(a) 50 : 50
(b) 30 : 70
(c) 70 : 30
(d) 40 : 60
Ans: b
146. Corrosion resistance of steel is increased by
adding
(a) chromium and nickel
(b) nickel and molybdenum
(c) aluminium and zinc
(d) tungsten and sulfur
Ans: a
147. Corrundum contains more than 95%
(a) steel
(b) A12O3
(c) SiO2
(d) MgO
Ans: b
148. Alnico, an alloy used extensively for
permanent magnets contains iron, nickel, aluminium and cobalt in the following
ratio
(a) 50 : 20 : 20 : 10
(b) 40 : 30 : 20 : 10
(c) 50 : 20 : 10 : 20
(d) 30 : 20 : 30 : 20
Ans: a
149. If a refractory contains high content of
silicon, it means refractory is
(a) acidic
(b) basic
(c) neutral
(d) brittle
Ans: c
150. Bell metal contains
(a) 70% copper and 30% zinc
(b) 90% copper and 10% tin
(c) 85-92% copper and rest tin with little lead
and nickel
(d) 70-75% copper and rest tin
Ans: d
151. Which of the following is used for bearing
liner
(a) gun metal
(b) bronze
(c) bell metal
(d) babbit metal
Ans: d
152. The correct sequence for descending order of
machinability is
(a) grey cast iron, low carbon steel, wrought iron
(b) low carbon steel, grey cast iron, wrought iron
(c) wrought iron,low carbon steel, grey cast iron
(d) wrought iron, grey cast iron, low carbon steel
Ans: a
153. Structural steel contains following principal
alloying elements
(a) nickel, chromium and manganese
(b) tungsten, molybdenum and phosphorous
(c) lead, tin, aluminium
(d) zinc, sulphur, and chromium
Ans: a
154. Aluminium bronze contains aluminium and
copper in the ratio of
(a) 50 : 50
(b) 40 : 60
(c) 60 : 40
(d) 10 : 90
Ans: d
155. Bronze contains
(a) 70% copper and 30% zinc
(b) 90% copper and 10% tin
(c) 85-92% copper and rest tin with little lead
and nickel
(d) 70-75% copper and rest tin
Ans: b
156. Muntz metal contains copper and zinc in the
ratio of
(a) 50 : 50
(b) 40 : 60
(c) 60 : 40
(d) 20 : 80
Ans: c
157. Gun metal contains
(a) 70% copper and 30% zinc
(b) 90% copper and 10% tin
(c) 85-92% copper and rest tin with little lead
and nickel
(d) 70-78% copper and rest tin
Ans: c
158. Perminvar alloy having constant permeability
is an alloy of
(a) nickel, copper and iron
(b) nickel, copper and zinc
(c) copper, nickel and antimony
(d) iron, zinc and bismuth
Ans: a
159. The alloy used for making electrical
resistances and heating elements is
(a) nichrome
(b) invar
(c) magnin
(d) elinvar
Ans: a
160. Monel metal contains
(a) 63 to 67% nickel and 30% copper
(b) 88% copper and 10% tin and rest zinc
(c) alloy of tin, lead and cadmium
(d) malleable iron and zinc
Ans: a
163. Permalloy is a
(a) kind of stainless steel
(b) none ferrous alloy
(c) polymer
(d) cutting tool material
Ans: e
164. Phosphor bronze contains
(a) 0.5% of phosphorous
(b) 1% phosphorous
(c) 2.5% phosphorous
(d) 5% phosphorous
Ans: e
165. Free cutting steels
(a) are used where ease in machining is the
criterion
(b) contain carbon in free form
(c) require least cutting force
(d) do not exist
Ans: a
166. Delta metal is an alloy of
(a) copper, zinc and iron
(b) iron, nickel and copper
(c) iron, lead and tin
(d) iron, aluminium and magnesium
Ans: a
167. Admiralty gun metal contains
(a) 63 to 67% nickel and 30% copper
(b) 88% copper, 10% tin and rest zinc
(c) alloy of tin, lead and cadmium
(d) iron scrap and zinc
Ans: b
168. Which of the following alloys does not
contain tin
(a) white metal
(b) solder admiralty
(c) fusible metal
(d) phosphor bronze
Ans: a
169. Which is false statement about properties of
aluminium
(a) modulus of elasticity is fairly low
(b) wear resistance is very good
(c) fatigue strength is not high
(d) creep strength limits its use to fairly low
temperatures
Ans: b
170. Addition of copper to aluminium results in
(a) improvement of casting characteristics
(b) improvement of corrosion resistance
(c) one of the best known age and
precipitation-hardening systems
(d) improving machinability
Ans: c
171. Addition of manganese to aluminium results in
(a) improvement of casting characteristics
(b) improvement of corrosion resistance
(c) one of the best known age and
precipitation-hardening systems
(d) improving machinability
Ans: b
172. Elinvar, an alloy used in precision instruments,
hair springs for watches, etc. contains the following element as principal
alloying element
(a) iron
(b) copper
(c) aluminium
(d) nickel.
Ans: d
173. Which of the following alloys does not have
copper as one of the constituents
(a) delta metal
(b) monel metal
(c) constantan
(d) nichrome
Ans: d
174. Addition of lead and bismuth to aluminium
results in
(a) improvement of casting characteristics
(b) improvement of corrosion resistance
(c) one of the best known age and
precipitation-hardening systems
(d) improving machinability
Ans: d
175. Addition of silicon to aluminium results in
(a) improvement of casting characteristics
(b) improvement of corrosion resistance
(c) one of the best known age and precipitation-hardening
systems
(d) improving machinability
Ans: a
176. Constantant an alloy used in thermocouples is
an alloy of
(a) copper and tin
(b) copper and zinc
(c) copper and iron
(d) copper and nickel
Ans: d
177. White metal contains
(a) 63 to 67% nickel and 30% copper
(b) 88% copper and 10% tin and rest zinc
(c) alloy of tin, lead and cadmium
(d) silver and chromium
Ans: c
178. German silver contains
(a) 1% silver
(b) 2.5% silver
(c) 5% silver
(d) 10% silver
Ans: c
179. Which of the following has highest specific
strength of all structural materials
(a) magnesium alloys
(b) titanium alloys
(c) chromium alloys
(d) magnetic steel alloys
Ans: b
180. Dow metal contains
(a) 94% aluminium, 4% copper and 0.5% Mn, Mg, Si
and Fe
(b) 92.5% aluminium and, 4% copper, 2% nickel and
1.5% Mg
(c) 90% aluminium and 90% copper
(d) 90% magnesium and 9% aluminium with some
copper
Ans: d
183. Aluminium bronze contains
(a) 94% aluminium, 4% copper and 0.5% Mn, Mg, Si
and Fe
(b) 92.5% aluminium, 4% copper, 2% nickel, and
1.5% Mg
(c) 10% aluminium and 90% copper
(d) 90% magnesium and 9% aluminium with some
copper
Ans: c
184. Babbit metal is a
(a) lead base alloy
(b) tin base alloy
(c) copper base alloy
(d) (a) and
(c) above.
Ans: d
127. Large forgings, crank shafts, axles normally
contain carbon up to
(a) 0.05 to 0.20%
(b) 0.20 to 0.45%
(c) 0.45 to 0.55%
(d) 0.55 to 1.0%
Ans: c
128. Heavy duty leaf and coil spring* contain
carbon of the following order
(a) 0.2%
(b) 0.5%
(c) 0.8%
(d) 1.0%
Ans: d
129. Taps, dies and drills contain carbon
(a) below 0.5%
(b) below 1%
(c) above 1%
(d) above 2.2%
Ans: c
130. Drop forging dies contain carbon of the order
of
(a) 0.1 to 0.2%
(b) 0.25 to 0.5%
(c) 0.6 to 0.7%
(d) 0.7 to 0.9%
Ans: c
185. The correct composition of Babbit metal is
(a) 87.75% Sn, 4% Cu, 8% Sb, 0.25% Bi
(b) 90% Sn, 2% Cu, 4% Sb, 2% Bi, 2% Mg
(c) 87% Sn, 4% Cu, 8% Sb, 1% Al
(d) 82% Sn, 4% Cu, 8% Sb, 3% Al, 3% Mg
Ans: a
186. DuraJomin contains
(a) 94% aluminium, 4% copper and 0.5% Mn, Mg, Si
and Fe
(b) 92.5% aluminium, 40% copper, 2% nickel, and
1.5% Mg
(c) 10% aluminium and 90% copper
(d) 90% magnesium and 9% aluminium with some
copper
Ans: a
190. Following elements have face-centred cubic
structure
(a) gamma iron (910° to 1400°C), Cu, Ag, Au, Al,
Ni, Pb, Pt
(b) Mg, Zn, Ti, Zr, Br, Cd
(c) a iron (below 910°C and between 1400 to
1539°C), W
(d) all of the above
Ans: a
191. Recrystallisation temperature can belowered
by
(a) purification of metal
(b) grain refinement
(c) working at lower temperature
(d) all of the above
Ans: d
192. Pearlite is a combination of
(a) ferrite and cementite
(b) cementite and gamma iron
(c) ferrite and austenite
(d) ferrite and iron graphite
Ans: a
193. Austenite rs a combination of
(a) ferrite and cementite
(b) cementite and gamma iron
(c) ferrite and austenite
(d) ferrite and iron graphite
Ans: b
194. The transistor is made of
(a) silver
(b) gold
(c) copper
(d) germanium
Ans: d
195. Lead is poured into the joint between two
pipes. These pipes may
be made of
(a) cast iron
(b) vitrified clay
(c) asbestos cement
(d) concrete
Ans: a
112. Grey cast iron
(a) contains 1.7 to 3.5% carbon in free state and
is obtained by the slow cooling of molten cast iron
(b) is also known as chilled cast iron am is
obtained by cooling rapidly. It i: almost unmachinable
(c) is produced by annealing process. I is soft,
tough and easily machinec metal
(d) is produced by small additions o magnesium (or
cerium) in the ladle Graphite is in nodular or spheroida form and is well
dispersed throughout the material
Ans: a
113. Nodular iron has
(a) high maehinability
(b) low melting point
(c) high tensile strength
(d) all of the above.
Ans: d
114. Nickel in steel
(a) improves wear resistance, cutting ability and
toughness
(b) refines grain size and produces less tendency
to carburisation, improves corrosion and heat resistant proper¬ties
(c) improves cutting ability and reduces
hardenability
(d) gives ductility, toughness, tensile strength
and anticorrosion properties
Ans: d
138. Ductile cast iron
(a) contains 1.7 to 3.5% carbon in free state and
is obtained by the slow cooling of molten cast iron
(b) is also known as chilled cast iron and is
obtained by cooling rapidly. It is almost unmachinable
(c) is produced by annealing process. It is soft,
tough and easily machined metal
(d) is produced by small additions of magnesium
(or creium) in the ladle. Graphite is in nodular or spheroidal form and is well
dispersed throughout the material
Ans: d
107. Tensile strength of steel can be safely
in-creased by
(a) adding carbon up to 2.8%
(b) adding carbon up to 6.3%
(c) adding carbon up to 0.83%
(d) adding small quantities of copper
Ans: c
108. High carbon steel carries carbon %age c
(a) 0.1 to 0.3%
(b) 0.3 to 0.6%
(c) 0.6 to 0.8%
(d) 0.8 to 1.5%
Ans: d
109. Cobalt in steel
(a) improves wear resistance, cuttinability and
toughness
(b) refines grain size and produces les tendency
to carburisation, improve corrosion and heat resistant proper ties
(c) improves cutting ability and reduce
hardenability
(d) gives ductility, toughness, tensile strength
and anti corrosion
property:
Ans: c
110. The percentage of carbon in low carbon steel
is
(a) 0.05%
(b) 0.15%
(c) 0.3%
(d) 0.5%
Ans: b
91. Vanadium in high speed steels
(a) promotes decarburisation
(b) provides high hot hardness
(c) forms very hard carbides and thus in-creases
wear resistance
(d) promotes retention of austenite
Ans: c
92. Amorphous material is one
(a) in which atoms align themselves in a geometric
pattern upon solidification
(b) in which there is no definite atomic structure
and atoms exist in a random pattern just as in a liquid
(c) which is not attacked by phosphorous
(d) which emits fumes on melting
Ans: b
72. An engineer’s hammer is made of
(a) cast iron
(b) forged steel
(c) mild steel
(d) high carbon steel
Ans: d
73. Inconel is an alloy of
(a) nickel, chromium and iron
(b) nickel, copper
(c) nickel, chromium
(d) nickel, zinc
Ans: a
74. By severely deforming a metal in a particular
direction it becomes
(a) ductile
(b) malleable
(c) homogeneous
(d) anisotropic.
Ans: d
75. Solder is an alloy consisting of
(a) tin, antimony, copper
(b) tin and copper
(c) tin and lead
(d) lead and zinc
Ans: b
62. Railway rails are normally made of
(a) mild steel
(b) alloy steel
(c) high carbon
(d) tungsten steel
Ans: c
63. Pick up the wrong statement
(a) aluminium in steel results in excessive grain
growth
(b) manganese in steel induces hardness
(c) nickel and chromium in steel help in raising
the elastic limit and improve the resilience and ductility
(d) tungsten in steels improves magnetic
properties and hardenability
Ans: a
64. Pick up the wrong statement Nickel and
chromium in steel help in
(a) providing corrosion resistance
(b) improving machining properties
(c) providing high strength at elevated
temperatures
(d) raising the elastic limit
Ans: b
65. Machining properties of steel are improved by
adding
(a) sulphur, lead, phosphorous
(b) silicon, aluminium, titanium
(c) vanadium, aluminium
(d) chromium, nickel
Ans: a
66. Eutectoid steel contains following percentage
of carbon
(a) 0.02%
(b) 0.3%
(c) 0.63%
(d) 0.8%
Ans: d
67. The basic constituents of Hastelloy are
(a) aluminium, copper etc.
(b) nickel, molybdenum etc.
(c) nickel, copper, etc.
(d) all of the above
Ans: b
68. Basic constituents of Monel metal are
(a) nickel, copper
(b) nickel, molybdenum
(c) zinc, tin, lead
(d) nickel, lead and tin
Ans: a
69. German silver is an alloy of
(a) silver and some impurities
(b) refined silver
(c) nickel, copper and zinc
(d) nickel and copper
Ans: c
70. Surveying tapes are made of a material having
low coefficient of expansion and enough strength. The alloy used is
(a) silver metal
(b) duralumin
(c) Hastelloy
(d) invar.
Ans: d
60. The most effective inhibitor of grain growth,
when added in small quantities is
(a) carbon
(b) vanadium
(c) manganese
(d) cobalt
Ans: b
61. Depth of hardness of steel is increased by
addition of
(a) nickel
(b) chromium
(c) tungsten
(d) vanadium
Ans: b
117. Melting point of iron is
(a) 1539°C
(b) 1601°C
(c) 1489°C
(d) 1712°C
Ans: a
56. Maximum percentage of carbon in ferrite is
(a) 0.025%
(b) 0.06%
(c) 0.1%
(d) 0.25%
Ans: a
57. Maximum percentage of carbon in austenite is
(a) 0.025%
(b) 0.26%
(c) 0.8%
(d) 1.25%
Ans: e
58. Corrosion resistance of steel is increased by
addition of
(a) chromium and nickel
(b) sulphur, phosphorus, lead
(c) vanadium, aluminium
(d) tungsten, molybdenum, vanadium, chromium
Ans: a
18. Which of the following constituents of steels
is softest and least strong
(a) austenite
(b) pearlite
(c) ferrite
(d) cementlte
Ans: c
19. Which of the following represents the
allotropic forms of iron
(a) alpha iron, beta iron and gamma iron
(b) alpha iron and beta iron
(c) body centred cubic a-iron and face centred
cubic a-iron
(d) alpha iron, gamma from and delta iron
Ans: d
20. The following types of materials are usually
the most ductile
(a) face-centred cubic lattice
(b) body-centred cubic lattice
(c) hexagonal close-packed lattice
(d) all of the above
Ans: a
21. Pure iron is the structure of
(a) ferrite
(b) pearlite
(c) anstenite
(d) ferrite and cementite
Ans: a
22. The temperature at which ferromagnetic alpha
iron transforms to paramagnetic alpha iron is
(a) 770°C
(b) 910°C
(c) 1050°C
(d) below recrystallisation temperature
Ans: a
23. Gamma iron exits at following temperature
(a) room temperature
(b) near melting point
(c) between 1400°C and 1539°C
(d) between 910°C and 1400°C
Ans: d
24. Ferromagnetic alpha iron exists in temperature
range of
(a) below 723°C
(b) 770 – 910°C
(c) 910-1440°C
(d) 1400-1539°C
Ans: a
25. Paramagnetic alpha iron changes to gamma iron
at
(a) 770°C
(b) 910°C
(c) 1440°C
(d) 1539°C
Ans: b
26. A reversible change in the atomic structure of
steel with corresponding change in the properties is known as
(a) molecular change
(b) physical change
(c) allotropic change
(d) solidus change
Ans: c
27. The molecules in a solid move
(a) in a random manner
(b) in a haphazard way
(c) in circular motion
(d) back and forth like tiny pendulums
Ans: d
28. The crystal structure of gamma iron is
(a) body centred cubic
(b) face centred cubic
(c) hexagonal close packed
(d) cubic structure
Ans: b
29. The crystal of alpha iron is
(a) body centred cubic
(b) face centred cubic
(c) hexagonal close packed
(d) cubic structure
Ans: a
30. The metallic structure of mild steel is
(a) body centred cubic
(b) face centred cubic
(c) hexagonal close packed
(d) cubic structure
Ans: a
31. For the allotropic forms of iron, the points
of arrest are
(a) the points where no further change oc-curs
(b) constant for all metals
(c) the points where there is no further flow of
metal
(d) the points of discontinuity
Ans: d
139. Brass contains
(a) 70% copper and 30% zinc
(b) 90% copper and 10% tin
(c) 85-92% copper and rest tin with little lead
and nickel
(d) 70-75% copper and rest tin
Ans: a
32. The percentage of carbon in pig iron varies
from
(a) 0.1 to 1.2%
(b) 1.5 to 2.5%
(c) 2.5 to 4%
(d) 4 to 4.5%
Ans: d
33. The percentage of carbon in grey iron castings
usually varies between
(a) 0.5 to 1%
(b) 1 – 2%
(c) 2.5 to 4.5%
(d) 5 – 7%
Ans: c
34. Pig iron is the name given to
(a) raw material for blast furnace
(b) product of blast furnace made by reduction of
iron ore
(c) iron containing huge quantities of carbon
(d) iron in molten form in the ladles
Ans: b
14) At forging temperature when a
compressive force is applied on the material, it deforms
a. elastically
in the direction of least resistance
b. elastically in the
direction of maximum resistance
c. plastically in the
direction of least resistance
d. plastically in the
direction of maximum resistance
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|
ANSWER: (c) plastically in the direction of least
resistance
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1) Which of the following statements is/are true for
alloy steels?
a. They
contain carbon more than 1.7%
b. They are ductile
c. They have low resilience
and toughness
d. All of the above
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|
ANSWER: (b) They are ductile
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2) Which of the following is a
ferrous alloy?
a. Brass
b. Aluminum alloys
c. Cast steel
d. All of the above
3) Copper when alloyed with zinc is
known as
a. Brass
b. Bronze
c. Babbits
d. All of the above
4) The plastic materials which do
not undergo chemical change when heated are ____
a. Thermoplasts
b. Thermosets
c. Both a. and b.
d. None of the above
5) Which of the following is a
characteristic of Polytetra-flouro-ethylene?
a. High
coefficient of friction
b. Tough at high temperature
c. Resistance to chemical
attack
d. All of the above
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ANSWER: (c) Resistance to chemical attack
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35. The unique property of cast iron is its high
(a) malleability
(b) ductility
(c) surface finish
(d) damping characteristics
Ans: d
36. Cast iron is characterised by minimum of
following %age of carbon
(a) 0.2%
(b) 0.8%
(c) 1.3%
(d) 2%
Ans: d
37. In grey cast iron, carbon is present in the
form of
(a) cementite
(b) free carbon
(c) flakes
(d) spheroids
Ans: c
38. In nodular iron, graphite is in the form of
(a) cementite
(b) free carbon
(C) flakes
(d) spheroids
Ans: d
39. In malleable iron, carbon is present in the
form of
(a) cementite
(b) free carbon
(c) flakes
(d) nodular aggregates of graphite.
Ans: d
40. Wrought iron is
(a) hard
(b) high in strength
(c) highly resistant to corrosion
(d) heat treated to change its properties
Ans: c
41. Sulphur in pig iron tends to make it
(a) hard’
(b) soft
(c) ductile
(d) tough
Ans: a
42. Pick up wrong statement about wrought iron
(a) It contains carbon of the order of 0 to 0.25%
(b) It melts at 1535°C
(c) It is very soft and ductile
(d) It is made by adding suitable percent¬age of
carbon to molten iron
and subjecting the product to repeated hammering
and rolling.
Ans: d
43. Iron is
(a) paramagnetic
(b) ferromagnetic
(c) ferroelectric
(d) dielectric
Ans: b
44. A reversible change in the atomic structure of
the steel with a corresponding change in the properties is known as
(a) allotropic change
(b) recrystallisation
(c) heat treatment
(d) precipitation
Ans: a
45. Chilled cast iron has
(a) no graphite
(b) a very high percentage of graphite
(c) a low percentage of graphite
(d) graphite as its basic constituent of
composition
Ans: a
46. Cast iron has
(a) high tensile strength
(b) its elastic limit close to the ultimate
breaking strength
(c) high ductility
(d) all of the above
Ans: b
47. White cast iron contains carbon in the form of
(a) free carbon
(b) graphite
(c) cementite
(d) white carbon
Ans: c
48. In mottled cast iron, carbon is available in
(a) free form
(b) combined form
(c) nodular form
(d) partly in free and partly in combined state.
Ans: d
49. An important property of high silicon (12 –
18%) cast
iron is the high
(a) tenacity
(b) brittleness
(c) plasticity
(d) hardness.
Ans: d
50. An important property of malleable cast iron
in comparison to grey cast iron is the high
(a) compressive strength
(b) ductility
(c) carbon content
(d) hardness
Ans: b
51. Steel contains
(a) 80% or more iron
(b) 50% or more iron
(c) alloying elements like chromium, tungsten
nickel and copper
(d) elements like phosphorus, sulphur and silicon
in varying quantities
Ans: b
52. Carbon steel is
(a) made by adding carbon in steel
(b) refined from cast iron
(c) an alloy of iron and carbon with varying
quantities of phosphorus and sulphur
(d) extensively used for making cutting tools
Ans: c
53. Annealing of white cast iron results in
production of
(a) malleable iron
(b) nodular iron
(c) spheroidal iron
(d) grey iron
Ans: a
54. ‘Killed steels’ are those steels
(a) which are destroyed by burning
(b) which after their destruction are recycled to
produce fresh steel
(c) which are deoxidised in the ladle with silicon
and aluminium
(d) in which carbon is completely burnt
Ans: c
118. Compressive strength of grey cast iron in
tonnes/cm is of the
order of
(a) 3- 5
(b) 5-7
(c) 7-10
(d) 10-15
Ans: b
121. The machinability of steel is increased by
(a) silicon and sulphur
(b) phosphorous, lead and Sulphur
(c) sulphur, graphite and aluminium
(d) phosphorous and aluminium
Ans: b
122. The following element can’t impart high
strength at elevated
temperature
(a) manganese
(b) magnesium
(c) nickel
(d) silicon
Ans: b
