A decimolar solution of ${\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$ at 300 K is 50% dissociated, then, osmotic pressure of the solution is

Standard solution is the term used to describe a solution whose strength is precisely known. Once more, a decimolar solution is one in which the strength is known when only one-tenth of a mole of a solute is present in a one-litre solution. Therefore, a standard solution is a decimolar solution.

$\underset{1-\mathrm{\alpha }}{{\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]}\rightleftharpoons \underset{4\alpha }{4{ \mathrm{K}}^{+}}+\underset{\alpha }{\left[\mathrm{Fe}\right(\mathrm{CN}){]}^{4-}}$

$i=\frac{1-\alpha /4\alpha +\backslash \alpha }{1}=1+4\alpha .$

$i=1+4\times 0.5=3$
 
$\pi =i\subset RT=3\times 0.1\times 0.0821\times 300=7.38 .$

Hence, the correct option (B). 7.38 atm