Q.Predict which of the following hydrides is a gas on a solid

The hydrides of group-13 elements, named after the family's first member boron, are called boranes (e.g. diborane, B$_2$H$_6$).

Group 13 (the boron family: B, Al, Ga, In, Tl) elements form electron-deficient hydrides, since each has only 3 valence electrons. Boron itself forms a range of covalent hydrides called boranes, the simplest stable one being diborane, B$_2$H$_6$ (BH$_3$ itself is unstable as a monomer and dimerises). This family name, 'boranes', is used generically for group-13 hydrides.

Groups 15, 16, and 17 form covalent, molecular hydrides (like $NH_3$, $H_2O$, HF) — small discrete molecules held together by covalent bonds, as opposed to the ionic hydrides of s-block metals or the metallic/interstitial hydrides of d-block metals.

Step 1 — Recall hydride classification: Hydrogen compounds (hydrides) are broadly classified into three types based on bonding: (i) Ionic (saline) hydrides — formed by highly electropositive s-block metals (e.g. NaH, $CaH_2$), where hydrogen exists as $H^-$;

(ii) Covalent (molecular) hydrides — formed by p-block non-metals;

(iii) Metallic (interstitial) hydrides — formed by d- and f-block metals, where H atoms occupy interstitial sites in the metal lattice.

Step 2 — Where groups 15–17 fit: Elements of groups 15 (N, P, As...), 16 (O, S, Se...), and 17 (F, Cl, Br...) are non-metals/metalloids that share electrons with hydrogen through covalent bonds, forming discrete small molecules such as $NH_3$, $PH_3$, $H_2O$, $H_2S$, HF, and HCl — these are covalent (molecular) hydrides.

Step 3 — Their typical properties: Being molecular (not extended ionic lattices), these hydrides are generally volatile, low-boiling compounds at room temperature, and many are gases.