Correct ray diagram from the following is

Which one of the following pair is larger in size.

${\mathrm{Fe}}^{2+},{\mathrm{Fe}}^{3+}$

Identify Dobereiner’s triads from the following groups of elements having similar chemical properties.
1. $\mathrm{Mg} (24.3), \mathrm{Ca} (40.1), \mathrm{Sr} (87.6)$

2. $\mathrm{S}(32.1), \mathrm{Se}(79.0), \mathrm{Te}(127.6)$

3. $\mathrm{Be}(9.0), \mathrm{Mg}(24.3), \mathrm{Ca}(40.1)$

Atomic symbols of first 20 elements of the periodic table are jumbled in a circle.

(i) Rearrange these elements in the increasing order of their atomic numbers.

(ii) Arrange these elements in their correct periods.

(iii) Arrange these elements in their correct groups.