(i) Ferrites are magnetic material. 
(ii) They are used in telephones and memory loops in computers.

(i) \(r=k[R]^n\)
When concentration is increased three times, [R] = 3a
\(27r=k(3a)^n\)
\(\frac{27r}{r}=\frac{k(3a)^n}{ka^n}or27\)
\(=​​​​​​​3^n \ or \ 3^3=3^n\)
\(\Rightarrow\ n=3\)
(ii) According to Arrhenius equation,
\(\log k=\log A-\frac{E_a}{2.303RT} \)
For uncatalysed reaction 
\(\log k=\log A-\frac{E_a(2)}{2.303RT}\ \ \ \ \ \ .......(i) \)
For catalysed reaction
\(\log k_2=\log\ A \frac{E_a(2)}{2.303RT}\ \ \ \ \ ....(ii)\)
A is equal for both the reactions.
Subtracting equation (i) from equation (ii)
\(\log\frac{k_2}{k_1}=\frac{E_a(1)-E_a(2)}{2.303RT}\)
\(\Rightarrow\ \log\frac{k_2}{k_1}=\frac{(75.2-50.14)kJ\ mol^{-1}}{2.303\times8.314\ JK^{-1}\ mol^{-1}\times 298 K}\)
\(\Rightarrow\ \log\frac{k_2}{k_1}=4.39\)
\(\Rightarrow\ \frac{k_2}{k_1}=antilog(4.39)\)
\(=2.45\times 10^4\)
Rate of reaction increases by 2.45 x 10⁴ times.

(i) Mira's father is right as it prevents the iron rods from corrosion.
(ii) Galvanization and cathodic protection.
(iii) Fe₂O₃.x H₂O
(iv) Scientific knowledge and care for his property.

(a) (i) The ratio of number of moles of one component to the total number of moles of solution is known as mole fraction.
(ii) The solution which follows Raoult's law over entire range of concentrations at specific temperature is called ideal solution.
(b) W_B = 15 g, W_A = 450 g, \(\Delta\)T_f = 0.34 K, M_B = ?
\({ M }_{ B }=\frac { 1000\times { K }_{ f }\times { W }_{ B } }{ \Delta { T }_{ f }\times { W }_{ A } } \)
\(=\frac { 1000\times 1.86 \ K \ kg \ { mol }^{ -1 }\times 15 \ g }{ 0.34K\times 450 \ g } \)
= 182.35 g/mol

(i) Since compound A (C₄H₁₀O) does not react with Na metal or KMnO₄, it cannot be an alcohol.
(ii) Since compound A dissolves in cone, H₂SO₄, it may be an ether.
(iii) Since ether A on heating with excess of HI gives a single alkyl halide, therefore, ether (A) must be symmetrical. Now the only symmetrical ether having M.F. C₄HIOO is diethyl ether (CH₃CH₂OCH₂CH₃).

(i) Since compound (E) with molecular formula, C₃H₆0 does not reduce Tollens' reagent and Fehling's solution but forms 2, 4-dinitrophenylhydrazone, it must be a ketone. But the only possible ketone having the molecular formula, C₃H₆O is acetone or propanone. Thus, compound (E) is acetone or (propanone) CH₃COCH3·
(ii) Since acetone (E) is obtained by heating compound (8) with Ca(OH)₂ therefore, (B) must be acetic acid (ethanoic acid), CH₃COOH.
(iii) Since (D) on oxidation with KMn04 gives acetic acid (8), therefore, (D) must be ethyl alcohol (ethanol), CH₃CH₂OH.
(iv) Since acetic acid (8) and ethyl alcohol (D) are obtained by hydrolysis of (C) under acidic conditions, therefore, (C) must be ethyl acetate (ethyl ethanoate), CH₃COOC₂H₅
(v) Since ethyl acetate (C) and acetic acid (8) are obtained by treatment of compound (A) with ethyl alcohol, therefore, compound (A) must be acetic anhydride (ethanoic anhydride), (CH₃COO)₂O.
(vi) All the reactions involved in this problem can now be explained as follows

(i) \(2Fe^{3+}+2I^-\longrightarrow2Fe^{2+}+I_2\)
\(E^0_{cell}=E^0_{I_2/ I^-}-E^0_{Fe^{3+}/Few^{2+}}=0.54 V - (0.77 V) = 0.54 V - 0.11 v = - 0.23 V\)
It is not feasible therefore E⁰_cell is -ve ΔG^o = +ve
(ii) 2Ag⁺(aq) + Cu(s) ⟶ Cu²⁺(aq) + Ag(s)
\(E^0_{cell} = E^0_{Ag^+/Ag} -E^0_{Cu^{2+}/Cu} = +0.80 V - 0.34 V = 0.46 V\)
It is feasible because E⁰_cell is +ve
∴ ΔG⁰ = - ve
(iii) 2Fe³⁺(aq) + 2Br^-(aq) ⟶ 2Fe²⁺(aq) + Br₂'
\(E^0_{cell} = E^0_{Fe^{3+}/Fe^{2+}}- E^0_{Br_2/Br^-} = 0.77 V - 1.09 V = - 0.32 V\)
Since E⁰_cell is -ve, ΔG^o = +ve therefore, reaction is non spontaneous.
(iv) Ag(s) + Fe³⁺(aq) ⟶ Fe²⁺(aq) + Ag⁺(aq)
\(E^0_{cell} = E^0 _{Fe^{3+}/Fe^{2+}}-E^0_{Ag^+/Ag} = 0.77 V - 0.80 V = - 0.03 V\)
since E⁰_cell is -ve, ΔG^o is +ve therefore, reaction is non spontaneous.
(v) Br₂ + 2Fe²⁺(aq) ⟶ 2Br^-(aq) + 2Fe³⁺(aq)
\(E^0_{cell} = E^0_{Br^2/Br^-} E^0_{Fe^{3+}/Fe^{2+}}=1.09 V - 0.77 V = 0.32 V\)
Since E⁰_cell is +ve, ΔG^o = -ve, therefore, reaction will be spontaneous.

(a) It is due to irregular variations in sum of first and second ionisation energies and sublimation energies. It is also due to stability of electronic configuration.
(b) (i) Cr₂O₇^2- + 3Sn²⁺ + 14H⁺➝ 2Cr³⁺ + 3Sn⁴⁺ + 7H₂O
(ii) MnO₄^- + 5Fe²⁺ + 8H⁺ ➝ SFe³⁺ + Mn²⁺ + 4H₂O