a) What are groups and period in the periodic table?
b) Two element M and N belong to group I and II respectively and are in the same period of the periodic table. How do the following properties of M and N vary?
1) Size of their atoms
2) This metallic characters
3) Their valencies informing oxides.
4) Molecular formulae of their chlorides.

Explanation

a) The vertical columns in the periodic table are called group. The horizontal rows in the periodic table are called periods.
b) 1. M and N belong to the same period but group I and Ii. Therefore N will be smaller than M as a atomic size is decreases from left to right.
2. M is more metallic than N. Metlallic character goes on decreasing from left to right as tendency to lose electrons.
3.Their valencies are 1 and 2 respectively in forming oxides. Valency goes on increasing first and then decreases.
4. MCI, `NCI_2` are molecules formulae of their chlorides.