a
(a) Inside the shell \(A\), electric field \(E_{in} = 0\)
At the surface of shell \(A\),
\({E_A} = \frac{{k\,{Q_A}}}{{r_A^2}}\) \(\xrightarrow{\,}\) (a fixed positive value)
Between the shell \(A\) and \(B\), at a distance \(x\) from the common centre
\(E = \frac{{k.\,{Q_A}}}{{{x^2}}}\) \(\xrightarrow{\,}\)  (as \(x\) increases \(E\) decreases)
At the surface of shell \(B\),
\({E_B} = \frac{{k.\,({Q_A} - {Q_B})}}{{r_B^2}}\) \(\xrightarrow{\,}\) (a fixed negative value because \(|QA| < |QB|)\)
Outside the both shell, at a distance \(x\) from the common centre
\({E_{out}} = \frac{{k({Q_A} - {Q_B})}}{{x{'^2}}}\) \(\xrightarrow{\,}\)  (as \(x\) increases negative value of Eout decreases and it becomes zero at \(x = \infty\))