Ncert Solutions Chemistry Class 11th

1.2 Molar mass of Na₂SO₄= (2 x Atomic mass of Sodium) + Atomic mass of Sulphur + (4 x Atomic mass of Oxygen)

= (2x 23) + 32 + (4x 16)

= 46 + 32 + 64

= 142 g/mol

In BF₃, boron is sp² hybridized.
? shape of BF₃ = planar.
In [BH₄]^–, boron is sp3 hybridized, thus the shape is tetrahedral.

On heating boric acid above 370 K, it forms metaboric acid, HBO₂ which on further heating yields boric oxide B₂O₃.

H₃B₂O₃ → HBO₂ → B₂O₃

Boric acid is a Lewis acid since it accepts electrons from hydroxyl ion of H₂O molecule. It is not a protic acid.
B (OH)₃ + 2HOH → [B (OH)₄]^– + H₃O⁺

In BCl₃, there is only six electrons in the valence shell of B atom. Thus, the octet is incomplete and it can accept a pair of electrons from water and hence BCl₃ undergoes hydrolysis. Whereas, in CCl₄, C atom has 8 electrons and its octet is complete. That's why it has no tendency to react with water.

In BF₃, central atom has only six electrons after sharing with the electrons of the F
atoms. It is an electron-deficient compound and thus behaves as a Lewis acid.

BCl₃ is quite stable. Because there is absence of d- and f-electrons in boron three valence electrons (2s² 2p_x1) are there for bonding with chlorine atom. In Tl the valence s-electron (6s²) are experiencing maximum inert pair effect. Thus, only 6p¹ electron is available for bonding. Therefore, BCl₃ is stable but TlCl₃ is comparatively unstable.

(i) B to Tl
Common oxidation states are +1 and +3. The stability of +3 oxidation state decreases from B to Tl while +1 oxidation state increases from B to Tl.

(ii) C to Pb
The common oxidation states are +4 and +2. Stability of +4 oxidation state decreases from C to Pb.

(d) BaCO₃

Thermal stability is directly proportional to the size of the cation i.e., larger the size of the atom, greater is its thermal stability. Ba being the biggest cation among the given compounds, has a greater thermal stability.