Which of the following half-reactions (acidic medium) are correctly balanced in both atoms and charge?

A $MnO X_{4} X^{-} + 8 H X^{+} + 5 e X^{-} Mn X^{2 +} + 4 H X_{2} O$
B $Cr X_{2} O X_{7} X^{2 -} + 12 H X^{+} + 6 e X^{-} 2 Cr X^{3 +} + 6 H X_{2} O$
C $NO X_{3} X^{-} + 4 H X^{+} + 2 e X^{-} NO + 2 H X_{2} O$
D $ClO X_{3} X^{-} + 6 H X^{+} + 6 e X^{-} Cl X^{-} + 3 H X_{2} O$

Answer: A, D

Check charge on both sides. (a): left -1+8-5 = +2, right +2, correct. (b): O count is 7 on the left but 6 on the right, so it is wrong (

14 H X^{+}

and

7 H X_{2} O

are needed). (c): left -1+4-2 = +1, right 0, so 3 electrons are needed. (d): left -1+6-6 = -1, right -1, correct.