In the Haber’s process the equivalent weight of ammonia is: (Molecular weight of ammonia = M)
                   (A) M
                   (B) M/3
                   (C) 2M/3
                   (D) 3M

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Hint: Haber’s process is a commercial process for manufacture of ammonia from nitrogen and hydrogen. Also, equivalent weight is the molecular weight divided by the n-factor of the reaction. So, find the n-factor by first finding out the change in oxidation state of nitrogen in the reaction involved.

Complete answer:
-First we need to see what equivalent weight is.
Equivalent weight is defined as the weight of a given substance that will combine with a given quantity of a given substance. It can also be defined as the mass obtained by dividing the molecular weight of a substance by its acidity or basicity (n-factor).
                                              $Eq.wt. = \dfrac{{Mol.wt.}}{{n - factor}}$
-Now let us see what Haber’s process is.
Haber’s process is an effective industrial process for manufacturing or producing ammonia. In this process atmospheric nitrogen (${N_2}$) is reacted with hydrogen (${H_2}$) and converted into ammonia ($N{H_3}$). This reaction takes place in the presence of a metal catalyst and under pressure (200-400 atm) and temperature (${500^ \circ }C$). In reaction form it is written as:
                                    $3{H_2} + {N_2} \rightleftharpoons 2N{H_3}$
In this process nitrogen is initially present in the form of ${N_2}$ and gets converted into $N{H_3}$ (ammonia).
-To find out the equivalent weight of ammonia:
For ${N_2}$ the oxidation state of N is 0 and in $N{H_3}$ it is (-3).
So, the change in oxidation state will be = 0 – (-3)
                                                                       = 3
The change in oxidation state is the n-factor and hence n-factor will be = 3.
So, we can now calculate the equivalent weight by putting the value of n-factor in the formula. It will be: $Eq.wt. = \dfrac{M}{3}$
So, the correct answer is “Option B”.

Note: Iron catalyst is used in this process because it is cheap and gives good quantity yield in less amount of time. This process is mainly used to form fertilizers and it produces 500 million tons of fertilizers every year that helps feed 40% of the human population.