The sum of number of protons and number of neutrons present in the nucleus of an atom is called its

1. mass number
2. atomic number
3. valency
4. none of these

The correct electronic configuration of sodium is:

1. 2, 8, 1
2. 1, 2, 8
3. 8, 2, 1
4. 8, 1, 2

Assertion (A): An atom is electrically neutral.

Reason (R): The number of protons and the number of electrons are equal in an atom.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): The nucleus of an atom is a centrally located mass containing protons only.

Reason (R): The nucleus of an atom is positively charged.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.