Write the balanced chemical reactions of the following reagents on carbolic acid (concentrated HNO₃ and Br₂ water).
a) 2C₆H₆ + 6HNO₃ → 2C₆H₄(NO₂)₃ + 6H₂O
b) C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O
c) C₆H₆ + 3HNO₃ → C₆H₅NO₃ + 3H₂O
d) 2C₆H₆ + 3HNO₃ → 2C₆H₄(NO₂)₃ + 3H₂O