Which of the following is an example of double displacement reaction?
(i) CO2(g)+H2(g)→CO(g)+H2O(g)
(ii) P4O10(s)+6H2O(l)→4H3PO4(aq)
(iii) H2+O2→H2O
(iv) CoCl2(aq)+Na2CO3(aq)→CoCO3(aq)+2NaCl(aq)
(iv)
In a double displacement reaction, the positive ions (cations) and the negative ions (anions) of the two reactants switch places, forming two new compounds or products.
In the equation,
CoCl2(aq)+Na2CO3(aq)→CoCO3(aq)+2NaCl(aq)
the anions Cl− & CO2−3 swap their places and form CoCO3 & 2NaCl,
hence it is an example of double displacement reaction.