Class 11th

This is a multiple choice type question as classified in NCERT Exemplar

Correct option (i) and (ii)

Beryllium resembles aluminum through the diagonal relation. Beryllium forms a protective film of oxide on the surface, and thus, is prevented by the attack of acids.

Thus, statement (1) is correct.

On moving down the group, as the size increases the hydration enthalpy decreases. The hydration enthalpy of beryllium ions are high due to the small size. Thus, sulfates are readily soluble in water. Thus, statement (2) is correct.

Beryllium does not exhibit coordination numbers more than four. As it has no d orbitals.

Thus, statement (3) is not correct.

Beryllium oxide is amphoteric in nature. It reacts with both acids and bases. It reacts with acid to form beryllium chloride and it reacts with base to form becyllate ion which is soluble in sodium hydroxide. The reaction is shown below.

Be (OH)₂+2OH−→ [Be (OH)₄]²⁻

Be (OH)₂+2HCl→BeCl₂+2H₂O

Thus, statement (4) is not correct.

This is a Long Answers Type Questions as classified in NCERT Exemplar

(i) Grp-13 The atomic size of the boron family follows the irregular trend. Generally, down the group the size increases but Gallium has a smaller atomic radius than Aluminium due to the poor shielding effect of 3d-orbitals.

Order: B

Grp-14 The size of the carbon family is smaller than the modern family and as we move down the group the atomic size increases regularly. The increase in covalent radius from carbon to silicon is prominent while from Silicon to lead a small increase in covalent radius is observed; this is due to the presence of completely filled D and f-orbital in the heavier members.

Order: C

(ii) Ionization enthalpy: In group 13, the standardised trend of decrease of Ionisation enthalpy is not monitored. 

As we move from Boron to Aluminium the atomic size increases and ionisation enthalpy decreases but when we move ahead from Aluminium to Gallium, the screening effect of 3d electrons comes into play. The poor shielding effect of the electrons lead to the increase in nuclear charge on the valence electrons and results in increase of ionisation enthalpy.

Moving from gallium to Indium, due to The shielding effect of 4d electrons the ionisation enthalpy decreases. 

From Indium to thallium, 4f electrons come into action their poor shielding effect increases the effective nuclear charge on valence electrons hence the ionisation of Thallium energy further increases. 

The decreasing order of ionization enthalpy for group-13 elements will be: B>Ti>Ga>Al>In

As we move down in group 14 the ionisation enthalpy decreases in the order: C>Si>Ge>Pb>Sn

On moving down the group the size of the atom increases which results in the large decrease in ionisation energy from carbon to silicon but as we move from silicon to heavier metals small decrease in the ionisation energy is observed. This is mainly due to the less screening effect of d-electrons in germanium and tin, and due to fully filled d & f electrons in lead.

(iii) Metallic character

The metallic character in group 13 follows an unusual trend. Metallic character First increases from Boron to aluminium and then decreases from aluminium to thallium. This decrease is majorly due to the poor shielding effect of d and f electrons present in the heavier metals.

In group-14, as we move down the group, the metallic character increases.

(iv) Possible oxidation states Group 13 elements are from +3 to -5. But the stability of +1 oxidation state increases down the group due to inert their effect than the stability of +3 oxidation state. 

Similarly, in group 14, The common oxidation states shown by the carbon family are +2 and +4. Due to the inert pair effect, stability of +2 oxidation state increases then the stability of +4.

(v) Except thallium, All the elements of the boron family combine with three atoms of halogens to form trihalides. All these halides exist as molecular species with hybridisation of sp². All the trihalides are Lewis acid and their acidic strength of trihalides of boron is in order: Bf₃33 hybridisation state and corresponding tetrahedral shape.

There are few exceptions also, SnF₄ and Pf₄ are ionic in nature, while the rest are covalent compounds.