Assertion : Beryllium resembles aluminium.

Reason : : Charge / radius of $B{e}^{2+}$ ion is nearly the same as that of the $A{l}^{3+}$ ion.

Assertion : As the electropositive character increases down the group, the stability of carbonates and hydrogen carbonates of alkali metals increases.

Reason : Lithium carbonates is not so stable to heat ; lithium being very small in size polarizes a large $C{O}_3^{2-}$ion leading to the formation of more stable $L{i}_{2}O$ and $C{O}_2$.

Assertion :  LiF is almost insoluble in water

Reason :  LiCl is soluble not only in water but also in acetone.

Assertion : s-block elements do not occur free in nature

Reason:  s-block elements are highly electropositive in nature.

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. Both A and R are false.

Assertion : Potassium and caesium are useful as electrodes in photoelectric cells.

Reason :  Potassium and caesium, when irradiated with light, the light energy absorbed is sufficient to eject out the electron from an atom.

Assertion :  The alkaline earth metals have much higher melting and boiling points than those of the alkali metals.

Reason : The melting and boiling points of alkaline earth metal do not vary in a regular fashion.

Assertion : The ionisation enthalpies of alkaline earth metals are fairly low.

Reason : In general, the low ionisation enthalpies of alkaline earth metals are due to large size of their atoms.