b
\((b)\) Sum of oxidation numbers of all atoms in a neutral molecule is zero.
\(\to A_3(B_4C)_2 : +2 \times 3 +2 \times [ 4 \times 5 -2] = 42 \neq 0\)
\(\to A_3(BC_4)_2 : +2 \times 3 +2 \times [ +5 -8) = 0\)
\(\to A_2(BC_3)_2 : +2 \times 2 + 2 \times [+5 -6) = +2 \neq 0\)
\(\to ABC_2 : +2 +5 +(-2) \times 2 = +3 \neq 0\)