c
According to question, electric field varies as

\(E=A r\)

Here \(r\) is the radial distance.

At \(r=a, E=A a.........(i)\)

Net flux emitted from a spherical surface of radius \(a\) is \(\phi_{\mathrm{net}}=\frac{q_{e n}}{\varepsilon_{0}}\)

\(\Rightarrow \quad(A a) \times\left(4 \pi a^{2}\right)=\frac{q}{\varepsilon_{0}} \quad[\text { Using equation }(\mathrm{i})]\)

\(\therefore \quad q=4 \pi \varepsilon_{0} A a^{3}\)