Consider the following ionization energies for an element X. X ( g ) → X ( g ) + Δ H = 1000 K J / m o l X ( g ) + → X ( g ) 2 + Δ H = 1900 K J / m o l X ( g ) 2 + → X ( g ) 3 + Δ H = 2914

Question

Consider the following ionization energies for an element X.

$X_{(g)} \to X_{(g)}^{+}$ $Δ H = 1000 K J / m o l$

$X_{(g)}^{+} \to X_{(g)}^{2 +}$ $Δ H = 1900 K J / m o l$

$X_{(g)}^{2 +} \to X_{(g)}^{3 +}$ $Δ H = 2914 K J / m o l$

$X_{(g)}^{3 +} \to X_{(g)}^{4 +}$ $Δ H = 4960 K J / m o l$

$X_{(g)}^{4 +} \to X_{(g)}^{5 +}$ $Δ H = 6273 K J / m o l$

$X_{(g)}^{5 +} \to X_{(g)}^{6 +}$ $Δ H = 21, 267 K J / m o l$

Which statement(s) is/are correct for the above given element?

TestHub · Accepted Answer

The significant jump in ionization energy between the 5th and 6th ionization energies ( $6273 K J / m o l$ to $21, 267 K J / m o l$ ) indicates that removing the 6th electron requires breaking into a stable, filled electron shell. This means the element has 5 valence electrons, placing it in Group 15.

A. Correct. With 5 valence electrons, it belongs to Group 15.

B. Correct. A trianion (X³⁻) would gain 3 electrons, achieving a stable octet configuration (5 + 3 = 8).

C. Incorrect. It has 5 valence electrons, not 6.

D. Correct. Cations decrease in size with increasing positive charge due to increased effective nuclear charge. Therefore, X⁵⁺ is larger than X⁶⁺.

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