76.Given below are two statements, labelled as Assertion (A) and Reason (R). In the context of the two statements, which of the following is correct ?Assertion (A) : Copper is extracted by smelting its sulphide ore.Reason (R) : The roasted sulphide ore contains copper sulphide and copper oxide.

77.Given below are two statements, labelled as Assertion (A) and Reason (R). In the context of the two statements, which of the following is correct ?Assertion (A) : High power electric lamps are usually filled with nitrogen gas.Reason (R) : The carbon filament has a limitation to reach the temperature to white heat without shortening the service life of the lamp.

78.Given below are two statements, labelled as Assertion (A) and Reason (R). In the context of the two statements, which of the following is correct ?Assertion (A) : Some plants flower only during spring season.Reason (R) : Day length affects flowering in plants.

79.Given below are two statements, labeled as Assertion (A) and Reason (R). In the context of the two statements, which of the following is correct ? 1. Assertion (A) : When a particle moving with a velocity collides elastically head on with a second particle of equal mass at rest, their velocities get exchanged. 2. Reason (R) : Kinetic energy is conserved in elastic collisions.

80.Given below are two statements, labelled as Assertion (A) and Reason (R). In the context of the two statements, which of the following is correct ?Assertion (A) : It is easier to drive a sharp needle through a piece of cloth or cardbord than to drive a blunt nail through the same materials.Reason (R) : The radius of the top of a sharp needle is much smaller than the radius of the tip of a blunt nail.