c
According to questions
\(l \propto \,{h^p}{c^q}{G^r}\)
\(l = k\,\,{h^p}\)        ..............(\(i\))
Writting dimensions of physical quantities on both sides 
\(\left[ {{M^0}L{T^0}} \right] = {\left[ {M{L^2}{T^{ - 1}}} \right]^p}{\left[ {L{T^{ - 1}}} \right]^q}{\left[ {{M^{ - 1}}{L^3}{T^{ - 2}}} \right]^r}\)
Applying the principle of homogeneity of dimensions we get

\(P - r = 0\)         .........(\(ii\))

\({2_p} + q + 3r = 1\)        ............(\(iii\))

\( - P - q - 2r = 0\)         ................(\(iv\))
Solving eqns. (\(ii\)), (\(iii\)), and (\(iv\)), we get
\(P = r = \frac{1}{2},q =  - \frac{3}{2}\)
From eqn.\(\left( i \right)\,l = \frac{{\sqrt {hG} }}{{_c3/2}}\)