Arrange the metal ions of the following compounds in increasing order…

The correct answer is Option (4) → (C), (A), (B), (D)

The oxidation number of the metal follows from the rule that the oxidation numbers in a neutral compound add up to zero, taking chlorine and fluorine as −1 and oxygen as −2:

    (A) \( \ce{TiCl3} \): \( x + 3(-1) = 0 \Rightarrow x = +3 \)
    (B) \( \ce{CrF6} \): \( x + 6(-1) = 0 \Rightarrow x = +6 \)
    (C) \( \ce{ZnO} \): \( x + (-2) = 0 \Rightarrow x = +2 \)
    (D) \( \ce{Mn2O7} \): \( 2x + 7(-2) = 0 \Rightarrow x = +7 \)

In increasing order:

    \( \displaystyle \ce{ZnO}\,(+2) \lt \ce{TiCl3}\,(+3) \lt \ce{CrF6}\,(+6) \lt \ce{Mn2O7}\,(+7) \)

So the order is (C), (A), (B), (D). Manganese reaches its highest oxidation state, +7, equal to its group number, in the oxide \( \ce{Mn2O7} \), and chromium reaches +6 with fluorine, the most electronegative element.

Shortcut: Zinc shows only +2, the lowest here, and manganese in \( \ce{Mn2O7} \) is +7, the highest. Only Option (4) starts with (C) and ends with (D).