Is Matter Around Us Pure — Science STD 9 — Question

The smell of hot sizzling food reaches you several meters away, but to get the smell of the cold food you have to go close.Which property of matter does this activity show:

For an element, Z = 9. The valency of this element will be:

1. 4
2. 2
3. 1
4. 3

Which of the following elements has the same molecular mass as its atomic mass?

1. Nitrogen.
2. Neon.
3. Oxygen.
4. Chlorine.

Molecular formula of potassium nitrate is:

The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called:

Smallest particle of an element or a compound which is capable of independent existence is called:

Two elements X and Y have valencies of 5 and 3, and 3 and 2, respectively. The elements X and Y are most likely to be respectively:

1. Copper and sulphur.
2. Sulphur and iron.
3. Phosphorus and nitrogen.
4. Nitrogen and iron.

Which of the following factors are responsible for the change in state of solid carbon dioxide when kept exposed to air?

1. Increase in pressure
2. Increase in temperature
3. Decrease in pressure
4. Decrease in temperature

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

In a sample of ethyl ethanoate (CH₃COOC₂H) the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?