Answer: (3) In
Explanation: As the given compound is \(X_2O_3\), it can be said that X has a valency of 3.
1)Barium (Ba): Atomic no: 56: \(Xe6s^2\) : In order to complete its octet, it needs to donate 2 electrons, and thus the valency is 2.
2) Cadmium (Cd) : Atomic no: 48: \(Kr5s^24d^{10}\) : In order to complete its octet, it needs to donate 2 electrons, and thus the valency is 2.
3) Indium (In): Atomic no: 49: \(Kr5s^25p^{1}\) : In order to complete its octet, it needs to donate 3 electrons, and thus the valency is 3.
4) Sodium (Na): Atomic no: 11: \(Ne3s^1\) : In order to complete its octet, it needs to donate 1 electron, and thus the valency is 1.
So the given element could only belong to the group containing Indium (In) as all the elements in the same group exhibit similar valency.
