D & F Block Elements MCQs for NEET — Chemistry Questions with Answers

Lead (II) oxide (PbO2) is the compound of lead used in the match industry. It acts as an oxidizing agent in the ignition mixture of match heads, providing the oxygen needed for combustion.

 Argon is also used to form inert atmospheres for arc welding,

growing semiconductor crystals and processes that require shielding from other atmospheric gases.

(a) CuSO⁴_(aq.)$\stackrel{{\mathrm{H}}_2\mathrm{S}\uparrow }{\to }$    2CuS        $\underset{excess}{\overset{\mathrm{KCN}}{\to }}$[Cu(CN)₄]^3-+(CN)2$\uparrow$

                             Black ppr.(M)                  (N)               (O)

(a) 2CrO₄^2-+ 2H⁺$\to$Cr₂O₇^2-+H₂O

     Cr₂O₇^2-+2OH^-$\to$2CrO₄^2-+H₂O

When steam is passed over red hot iron, the reaction that takes place is: 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g). Iron is oxidized to Fe3O4 (iron(II,III) oxide or magnetite), and hydrogen gas is evolved. This reaction is used in the industrial production of hydrogen gas.

(b) NaCl(s) + K₂Cr₂O₇ + H₂SO₄ (few drops)$\underset{\mathrm{reaction}}{\overset{\mathrm{Non} \mathrm{redox}}{\to }}$CrO₂Cl₂$\uparrow$+H₂O

CrO₂Cl₂ + OH^-_(aq.)$\to$CrO_4(aq)^2-+Cl^-+2H₂O

(c) 

Formation of a thin layer of oxide upon the surface of metal, which protects the inner surface of metal to come in direct contact of air or other chemicals for reaction.

In KMnO₄, Mn has no d-electron and colour is due to charge transfer spectra