448. Consider an ideal solution of components A and B. The entropy of mixing per mole of an alloy containing 50 wt% B is
A. R ln 2
B. -R ln 2
C. 3 R ln 2
D. -3R ln 2
✅ The correct answer is option A.
450. Which of the following heat treatment processes is used for softening the hardened material?
A. Normalising
B. Tempering
C. Annealing
D. None of these
✅ The correct answer is option B.
452. The instrument based on the following principle is used for the measurement of oxygen only in the flue gases.
A. Chemical absorption
B. Thermal conductivity
C. Infrared absorption
D. Paramagnetism
✅ The correct answer is option D.
454. Which of the following metals occurs in nature in their free metallic state?
A. Au & Ag
B. Pb & Zn
C. Cu & Ni
D. None of these
✅ The correct answer is option D.
456. Which of the following has the highest value of refractive index?
A. Brine (sea water)
B. Diamond
C. Distilled water
D. Glass
✅ The correct answer is option B.
420. A dummy activity is used in PERT network to describe the
A. Precedence relationship
B. Resource idleness
C. Resource restriction
D. Necessary time delay
✅ The correct answer is option A.
422. __________ wire is never used for making the heating element.
A. Nichrome
B. Kanthal
C. Invar
D. None of these
✅ The correct answer is option C.
424. Babbit lining is used on brass/bronze bearings to increase the
A. Antifriction properties
B. Compressive strength
C. Bearing resistance
D. Wear resistance
✅ The correct answer is option D.
426. Oxide layer formed on the non-ferrous metal surface after its annealing is
A. Removed by acid pickling
B. Hammered into the surface
C. Removed with coarse emery cloth
D. Left as such to protect the surface
✅ The correct answer is option A.
429. Maximum heat dissipation occurs from a steel wire (k = 0.5 W/m. k) of 15 mm diameter exposed to air (h = 20W/m² .k), when the insulation thickness is __________ mm.
A. 15
B. 25
C. 10
D. 30
✅ The correct answer is option B.