Fill in the following blanks in respect of an atom of an element:

What name is given to the pair of atoms such as?

What name is given to those isotopes which have unstable nuclei and emit various types of radiations?

Complete the following statements:

(a) Magnesium has 3 valence electrons in the ………… shell.

(b) The valency of nitrogen in N₂ molecule is ……….

(c) Isotopes have different mass numbers because their nuclei contain different number of ……….

(d) Some boron atoms have mass number 10 and some have mass number 11. These boron atoms with different mass number are called ……...

The nucleus of an atom has 5 protons and 6 neutrons. What would be the

(a) atomic number,

(b) mass number,

(c) the number of electrons, and

(d) the number of valence electrons, per atom of this element?