Concept:
Osmotic pressure is given by
\[
\boxed{\pi=iCRT}
\]
where \(i\) is the van't Hoff factor.
Step 1: Calculate the van't Hoff factor.
Potassium ferrocyanide dissociates as
\[
\mathrm{K_4[Fe(CN)_6]}
\rightarrow
4\mathrm{K^+}
+\mathrm{[Fe(CN)_6]^{4-}}
\]
Thus,
\[
n=5
\]
Since degree of dissociation,
\[
\alpha=0.5
\]
\[
i=1+\alpha(n-1)
\]
\[
=1+0.5(5-1)
=3
\]
Step 2: Calculate osmotic pressure.
Given,
\[
C=0.1\ \mathrm{M},\qquad
R=0.082,\qquad
T=300\ \mathrm{K}
\]
\[
\pi
=3\times0.1\times0.082\times300
=7.38\ \mathrm{atm}
\]
Step 3: Final conclusion.
\[
\boxed{7.38\ \mathrm{atm}}
\]
Hence, the correct option is \(\boxed{(C)}\).