Atoms and Molecules — Science STD 9 — Question

A particle P has 18 electrons, 20 neutrons and 19 protons. This particle must be:

1. A molecule.
2. A binary compound.
3. An anion.
4. A cation.

The common characteristic of suspension and colloidal solution is:

The formula of a compound is X₃Y. The valencies of elements X and Y will be respectively:

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

You are given the following substances with their boiling and melting points.

Substance	Boiling Point (ºC)	Melting Point (ºC)
A	-183	-219
B	445	119
C	78	-15

Point out the physical states of A, B and C at room temperature (30°C).

The correct increasing order of the boiling points of liquid oxygen, liquid argon and liquid nitrogen present in liquid air is:

1. Nitrogen, oxygen, argon.
2. Nitrogen, argon, oxygen.
3. Argon, oxygen, nitrogen.
4. Oxygen, argon, nitrogen.

Which of the following is not a mixture?

The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

Which of the following atom has a valency of three:

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.