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121.

In order to observe the grain size of steel samples under microscope, the magnification should be the order of

122.

If a sample of steel shown excessive hardness after tempering the probable cause could be

A.	Insufficient holding time during tempering	B.	Excessive proportion of alloying elements
C.	High temperature during tempering	D.	Change in volume during cooling
E.	None of the above

123.

There are 14 atoms in a unit cell of

A.	Body centred cubic space lattice	B.	Face centred cubic space lattice
C.	Close packed hexagonal space lattice	D.	All of the above
E.	None of the above

124.

Cracks of a vertical nature and dark coloured fissures in a sample of hardened steel indicate that

A.	Steel has been properly hardened	B.	Steel has not been properly heated
C.	Steel has been burned	D.	Steel has achieved maximum possible hardness in accordance with the carbon percentage
E.	Steel contains excessive alloying elements

125.

A chisel for cutting steel plates is usually

126.

On Moh's scale, materials with hardness number less than 4 are

A.	Topaz, Corundum, Diamond	B.	Talc, gypsum, calcite
C.	Fluorite, Felsper, Talc	D.	Felspar, corundum, Diamond

127.

The slowest cooling rate is achieved when steel is quenched in

A.	fused salt	B.	Air
C.	Brine	D.	mixture of water

128.

Warping may be avoided when quenching a long slender piece of work by

A.	Holding the work piece between clamps and pouring water on it	B.	Hoding the work piece vertically over the quenching bath and plunging it straight
C.	Pulling the piece from both ends	D.	Holding the piece horizontally in adequate supports
E.	None of the above

129.

Which colour of flame represents the highest temperature?

130.

The coordination number of NaCl is