The correct decreasing order of first ionisation enthalpies of five elements of the second period is
Be > B > C > N > F
N > F > C > B > Be
F > N > C > Be > B
N > F > B > C > Be
C.
F > N > C > Be > B
In general, as we move from left to right in a period, the ionisation enthalpy increases with increasing atomic numbers. But the ionisation enthalpy of Boron (B) is lower than that of Beryllium (Be). This is due to the electronic configuration of B(1s2 2s2 2p1) which is less stable than that of Be (1s2 2s2) which has completely filled orbitals.
Thus, the correct order is F > N > C > Be > B
In which of the following the oxidation number of oxygen has been arranged in increasing order?
OF2 < KO2 < BaO2 < O3
BaO2 < KO2 < O3 < OF2
BaO2 < O3 < OF2 < KO2
KO2 < OF2 < O3 < BaO2
In which one of the following pairs the radius of the second species is greater than that of the first?
Na, Mg
O2-, N3-
Li+, Be2+
Ba2+, Sr2+
The lattice enthalpy and hydration enthalpy of four compounds are given below
| Compound | Lattice enthalpy (in kJ mol-1) | Hydration enthalpy (in kJ mol-1) |
| P | +780 | -920 |
| Q | +1012 | -812 |
| R | +828 | -878 |
| S | +632 | -600 |
The pair of compound which is soluble in water is
P and R
Q and R
P and Q
Rand S
The electronic configuration of the element with maximum electron affinity is
1s2, 2s2,2p3
1s2, 2s2,2p5
1s2, 2s2,2p6, 3s2, 3p5
1s2, 2s2,2p6, 3s2, 3p3
| Column I | Column II | ||
| (A) | He | (i) | High electron affinity |
| (B) | Cl | (ii) | Most electropositive element |
| (C) | Ca | (iii) | Strongest reducing agent |
| (D) | Li | (iv) | Highest ionisation energy |
A-iv, B-i, C-ii, D-iii
A-iii, B-i, C-ii, D-iv
A-iv, B-iii, C-ii, D-i
A-ii, B-iv, C-i, D-iii
The first () and second (ΔH2) ionisation enthalpies (in kJ mol-1) and the (ΔegH) electron gain enthalpy (in kJ mol-1) of the elements I, II, III, IV and V are given below
| Element | ΔH1 | ΔH2 | ΔegH |
| I | 520 | 7300 | -60 |
| II | 419 | 3051 | -48 |
| III | 1681 | 3374 | -328 |
| IV | 2372 | 5251 | +48 |
The most reactive metal and the least reactive non-metal of these are respectively
I and IV
IV and II
II and IV
III and IV
'Hydride Gap' is referred to which region of the Periodic Table ?
Groups 3, 4 and 5
Groups 5, 6 and 7
Groups 4, 5 and 6
Groups 7, 8 and 9
The first ionisation energy of oxygen is less than that of nitrogen. Which of the following is the correct reason for this observation?
Lesser effective nuclear charge of oxygen than nitrogen.
Lesser atomic size of oxygen than nitrogen
Greater interelectron repulsion between two electrons in the same p-orbital counter balances the increase in effective nuclear charge on moving from nitrogen to oxygen.
Greater effective nuclear charge of oxygen than nitrogen.
