Which of the following are contact forces ?

A. Friction B. Gravitational force

C. Magnetic force D. Muscular force

When we press the bulb of a dropper with its nozzle kept in water air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to :

A rectangular wooden block has length, breadth and height of 50 cm, 25 cm and10 cm, respectively. This wooden block is kept on ground in three different ways, turn by turn. Which of the following is the correct statement about the pressure exerted by this block on the ground?

If we release a magnet held in our hand, it falls to the ground. The force responsible for this is :

Which of the following force is utilized in reducing air pollution by removing dust, soot and fly-ash particles from the smoke coming out of chimneys of factories ?