<p>(a) Give reasons:</p>

<p>(i) Transition metals and their compounds show catalytic acitivities.</p>

<p>(ii) Separation of a mixture of Lanthanoid elements is difficult.</p>

<p>(iii) Zn, Cd and Hg are soft and have low melting points.</p>

<p>(b) Write the preparation of the following:</p>

<p>(i)&nbsp;<span class="equation">\(Na_2Cr_2O_7\)</span>&nbsp;from <span class="equation">\(Na_2CrO_4\)</span>​​​​​​​</p>

<p>(ii)&nbsp;<span class="equation">\(K_2MnO_4\)</span>&nbsp;from <span class="equation">\(MnO_2\)</span>​​​​​​​​​​​​​​</p>