For the second-period elements, the correct increasing order of first ionisation enthalpy is:

1.	Li < Be < B < C < O < N < F < Ne
2.	Li < Be < B < C < N < O < F < Ne
3.	Li < B < Be < C < O < N < F < Ne
4.	Li < B < Be < C < N < O < F < Ne

Amongst the elements with the following electronic configurations, which one of them may have the highest ionisation energy?

1. $\left[Ne\right]$ $3s^2$ $3p^2$

2. $\left[Ne\right]$ $3s^2$ $3p^3$

3. $\left[Ar\right]$ $3d^{10}$ $4s^2$ $4p^3$

4. $\left[Ne\right]$ $3s^2$ $3p^1$

Which of the following ionic species is isoelectronic with \(\mathrm{Be^{2+}}\)?

Which of the following represents the correct order of ionic radii?

The species Ar, K⁺ and Ca²⁺ contain the same number of electrons. In which order do their radii increase?
1.  Ar < K⁺ < Ca²⁺
2. Ca²⁺ < Ar < K⁺
3. Ca²⁺ < K⁺ < Ar
4. K⁺ < Ar < Ca²⁺

The formation of the oxide ion, O²⁻(g), from an oxygen atom occurs in two successive steps:

O(g) + e⁻ → O⁻(g)  ΔH = −141 kJ mol⁻¹

O⁻(g) + e⁻ → O²⁻(g)  ΔH = +780 kJ mol⁻¹

Although O²⁻ is isoelectronic with neon, its formation in the gaseous state is energetically unfavourable. What is the main reason for this?

Which of the following triads do not follow Dobereiner's law of triads? 

The correct trend of atomic size among the following is:

 1. F > N > O > C

 2. Rb > Na > K > Li

 3. Be > B > C > N

 4. Ne >He > Ar > Kr