JEE Main 2023 · 8 April · morning · Single correct · +4 / −1

2 IO₃⁻+x I⁻+12 H⁺ → 6 I₂+6 H₂ O
What is the value of x ?

  1. (a) 10
  2. (b) 2
  3. (c) 12
  4. (d) 6
Answer and solution

Answer (a) 10

Solution

Chemistry ma’am · 4 steps

Every iodine on the right came from somewhere on the left, so count iodine atoms and check with charge.

  1. Count iodine atoms. The right side has 6 I₂, that is 12 iodine atoms. The left side has 2 from IO₃⁻ and x from I⁻, so 2 + x = 12 and x = 10.
  2. Check the charge. Left side: 2(-1) + x(-1) + 12(+1) = 10 - x. Right side: I₂ and H₂O are neutral, so the charge is 0. Setting 10 - x = 0 again gives x = 10.
  3. Check electrons. Iodine in IO₃⁻ goes from +5 to 0, so 2 iodate ions gain 2 × 5 = 10 electrons. Each I⁻ goes from -1 to 0 and loses 1 electron, so 10 iodide ions are needed to supply them.
  4. So. All three checks agree: x = 10, option (a).

The idea to keep. In a balanced redox equation, atoms, charge and electrons must all balance. If one coefficient is missing, use whichever is quickest, then confirm it with another.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Redox Reactions

Asked about 90 times in JEE Main since 2020. This question is from 2023.