To obtain the powerful parallel beams of light from a vehicle's headlight, one must use

• front surface silvered plane mirror

• back surface silvered plane mirror

• concave mirror

• convex mirror

A fan produces a feeling of comfort during hot weather, because

• our body radiates more heat in air

• fan supplies cool air.

• conductivity of air increases

• our perspiration evaporates rapidly

Which one among the following denotes the smallest temperature?

• 1° on the Celsius scale

• 1° on the Kelvin scale

• 1° on the Fahrenheit scale

• 1° on the Reaumur scale.

84.

Which one among the following methods is not effective in removing arsenic from contaminated groundwater?

• Boiling

• Reverse osmosis

• Ion exchange

• Coagulation-adsorption