An element $X$ has successive ionisation enthalpies (in $kJ mo l^{- 1}$ ) of 590, 1145, 4912 and 6491. The stable oxide of $X$ and the reason are best given by

A $XO X_{2}$ , because the fourth value is close to the third
B $XO$ , because a huge jump occurs after $Δ_{i} H_{2}$ , showing two valence electrons
C $X X_{2} O$ , because $Δ_{i} H_{1}$ is the smallest value
D $X X_{2} O X_{3}$ , because three electrons are removed below $5000 kJ mo l^{- 1}$

Answer: B

Ratios: 1145/590 is about 1.9, but 4912/1145 is about 4.3, a large jump after the second electron. The third electron comes from an inner core, so X shows oxidation state +2 and forms

XO

. The fourth value (6491) is only a modest increase over the third.

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An element X has successive ionisation enthalpies (in kJ mol−1) of 590, 1145, 4912 and 6491. The stable oxide of X and the reason are best given by

Answer: B

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An element $X$ has successive ionisation enthalpies (in $kJ mo l^{- 1}$ ) of 590, 1145, 4912 and 6491. The stable oxide of $X$ and the reason are best given by