Question

The oxide of nitrogen which forms dimer is:
A.) nitrogen oxide
B.) nitrous oxide
C.) nitrogen dioxide
D.) none of these

Answer 1

The dimer is a molecule in which two identical or similar molecules are linked or associated together. These identical or similar molecules may be linked together by covalent bonding or non-covalent bonding.

Complete step by step answer:
As we know that when nitrogen reacts with oxygen then it forms various compounds of oxides of nitrogen. In these oxides of nitrogen, the nitrogen exhibits different oxidation states that are ranging from $+ 1$ to $+ 5$.
In option A.), the given compound that is nitrogen oxide has the chemical formula as $NO$. It is a colorless gaseous compound. In the nitrogen oxide, nitrogen has the oxidation state of $+ 2$. $NO$ does not form any dimer.
In option B.), the given compound that is nitrous oxide has the chemical formula as $HN{O_3}$. In nitrous oxide, nitrogen has an oxidation number of $+ 5$. Nitrous acid ($HN{O_3}$) also does not form any dimer.
In option C.), the given compound that is nitrogen dioxide has the chemical formulas as $N{O_2}$. IN nitrogen dioxide, the oxidation state of nitrogen is $+ 4$. It is paramagnetic (contains unpaired electrons) in nature. $N{O_2}$ dimerizes to form ${N_2}{O_4}$. When two molecules of nitrogen dioxide ($N{O_2}$) units dimerize through $N - N$ bonds formation then the odd electron on nitrogen combines with that of another molecule. Therefore, the resultant dimerized molecule that is (${N_2}{O_4}$) becomes paramagnetic in nature having no unpaired electrons in it.

Hence, option C.) is the correct answer.

Note:
As nitrogen when reacted with oxygen forms many nitrogen oxides. Remember that the nitrogen oxide in which the oxidation state of nitrogen is high will be more acidic than that oxide of nitrogen in which nitrogen has lower oxidation state.