Answer: C. Characteristic properties of transition elements include: (i) variable oxidation states, (ii) coloured compounds, (iii) often acting as catalysts, (iv) high melting points and densities.
(1) Fe + dilute HCl → \(\text{H}_2\): a reactive metal reacting with acid is a general metal property (Mg, Zn and Group I metals do the same). It does not illustrate anything specific to transition elements. ✗
(2) \(\text{NiCl}_2\) solution is green: a coloured compound — a characteristic transition metal property. ✓
(3) Cr has oxidation states +2, +3 and +6: variable oxidation states — another characteristic transition metal property. ✓
So 2 and 3 only: option C. Be careful with option (1) — reactivity with acid is shared by many metals and is not what marks something out as a transition element.
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