Matter in Our Surroundings — Science STD 9 — Question

Which of the following are chemical changes?

1. Decaying of wood.
2. Burning of wood
3. Sawing of wood
4. Hammering of nail into wood

1. (i) and (ii)
2. (ii) and (iii)
3. (iii) and (iv)
4. (i) and (iv)

The electrons revolve around the nucleus only in certain fixed paths called:

The smell of the deodorant sprayed  on one side of the room travels to the other side of the room.This proves that:

When a gas jar full of air is placed upside down on a gas jar full of bromine vapours, the red-brown vapours of bromine from the lower jar go upward into the jar containing air. In this experiment:

Find out the incorrect increasing/decreasing order in the following:

If the K and L shells of an atom are full, then what will be the total number of electrons in the atom?

Crude oil is purified using fractional distillation process. This method works on the principle of:

When water at 0°C freezes to form ice at the same temperature of 0°C, then it:

1. Absorbs some heat.
2. Releases some heat.
3. Neither absorbs nor releases heat.
4. Absorbs exactly 3.34 × 10⁵J/ kg of heat.

The molecular formula of potassium nitrate is ________.