Multiple Choice QuestionsThe second ionisation enthalpies of Li, Be, B and C are in order
Li > B > C > Be
Li > C > B > Be
Be > C > B > Li
B > C > Be > Li
A.
Li > B > C > Be
The ionisation enthalpy depend on the following factors.
(i) Half-filled or fully filled atomic orbitals are more stable than other incomplete orbitals.
(ii) Smaller the size of atom/ion, more is the ionisation energy (IE) For 2nd IE all elements have M+ configuraton.
| Total no.of electrons | Outermost configuration | |
| Li+(Z=3) | 2 | 1s2 (fully filled) |
| Be+(Z=4) | 3 | 2s1(has more size than carbon) |
| B+(Z=5) | 4 | 2s2 (full filled) |
| C+(Z=6) | 5 | 2s22p1 (small size) |
Hence, correct order for 2nd IE is Li+>B+>C+ >Be+ or Li > B > C > Be.
The first four ionisation enthalpy values of an element are 191 kcal mol-1 578 kcal mol-1 872 kcal mol-1 and 5962 kcal mol-1 .The number of valence electrons in the element is
1
2
3
4
The main product obtained when a solution of sodium carbonate reacts with mercuric chloride is
Hg(OH)2
HgCO3HgO
HgCO3
HgCO3.Hg(OH)2
Among the alkali metals cesium is the most reactive because :
its incomplete shell is nearest to the nucleus
it has a single electron in the valence shell
it is the heaviest alkali metal
the outermost electron is more loosely bound than the outer most electron of the other alkali metals
The correct order in which the first ionisation potential increases is
Na, K, Be
K, Na, Be
K, Be, Na
Be, Na, K
When carbon monoxide is passed over solid caustic soda heated to 200°C, it forms
Na2CO3
NaHCO3
HCOONa
CH3COONa
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