When acceptor impurities of concentration NA are added to a semiconductor crystal, where n is the electron density in the conduction band and p is the hole density in the valence band, the ionised acceptors are given as:a) \(\frac{{{N_A}}}{{1 + 4\exp \left( {\frac{{{E_A} - {E_F}}}{{kT}}} \right)}}\)b) \(\frac{{{N_A}}}{{1 - 4\exp \left( {\frac{{{E_A} - {E_F}}}{{kT}}} \right)}}\)c) \(\frac{{{N_A}}}{{1 + 4\exp \left( {\frac{{{E_D} - {E_F}}}{{kT}}} \right)}}\)d) \(\frac{{{N_A}}}{{1 - 2\exp \left( {\frac{{{E_D} - {E_F}}}{{kT}}} \right)}}\)Of these statements:

• A. (a) and (b) are wrong
• B. (a) is correct but (c) is wrong
• C. (c) is correct but (d) is wrong
• D. (d) is correct but (c) is wrong