Why falling liquid drops are spherical?

This is due to property of surface tension possessed by the liquids.This makes the surface area minimum. For a given volume, sphere has minimum surface area.

Why diethyl ether has higher vapour pressure than ethyl alcohol at a particular temperature?

This is because the intermolecular forces of attraction in ethyl alcohol are stronger than those present in diethyl ether.

Why liquid have a definite volume but no definite shape?

This is because the intermolecular forces are strong enough to hold the molecule together but not so strong as to fix them into definite positions (as in solids) instead, they possess fluidity and hence no definite shape.

Volume of a cylinder containing 10 marbles and gas is 1 litre at 2 atm pressure. Now pressure on the cylinder is increased to 4 atm, at which volume becomes 725 ml. Calculate volume of each marble.the

A gas occupied a volume of 250 ml at 700 mm Hg pressure and 25°C. What additional pressure is required to reduce the gas volume to its 4/5th value at the same temperature