Question

What is polling?

Hint: We come across the term ‘polling’ in metallurgy. It is a purification method. It is generally carried out for metals like copper or tin.

Polling or Poling is a method of purification for metals having their own oxide as impurity. We use polling generally to get rid of oxide impurities of the metal like copper oxide,$Cu{{O}_{2}}$ or tin oxide$Sn{{O}_{2}}$.
As we know, methane is a hydride of carbon and we can use carbon as a reducing agent. Thus, it acts as a reducing agent and reduces the metal oxide to give us the pure metal. $Cu{{O}_{2}}+C{{H}_{4}}(g)\to Cu(s)+CO(g)+{{H}_{2}}O(g)$
$Sn{{O}_{2}}+C{{H}_{4}}(g)\to Sn(s)+CO(g)+{{H}_{2}}O(g)$