One dimensional unsteady state hear transfer equation for a sphere with hear generation at the rate $q_{g}$ can be written as
(a) $\frac{1}{r}\frac{\partial }{\partial r}\left ( r\frac{\partial T}{\partial r} \right )+\frac{q}{k}=\frac{1}{\alpha }\frac{\partial T}{\partial t}$ 
(b) $\frac{1}{r^{2}}\frac{\partial }{\partial r^{2}}\left ( r\frac{\partial T}{\partial r} \right )+\frac{q}{k}=\frac{1}{\alpha }\frac{\partial T}{\partial t}$ 
(c) $\frac{\partial ^{2}T}{\partial r^{2}}+\frac{q}{k}=\frac{1}{\alpha }\frac{\partial T}{\partial T}$ 
(d) $\frac{\partial ^{2}}{\partial r^{2}}\left ( rT \right )+\frac{q}{k}=\frac{1}{\alpha }\frac{\partial T}{\partial t}$ 