Discussion
Assertion (A): Traces of iron or copper are far more damaging in peroxide bleaching than an equivalent amount of calcium.
Reason (R): They catalyse the decomposition of peroxide, so it is spent uselessly and attacks the fibre locally.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Iron and copper are transition metals that catalyse the breakdown of hydrogen peroxide into radicals, so the bleach is consumed before it can do its work and the radicals attack the cellulose at the point where the metal sits - producing pinholes and catalytic damage. A few parts per million matter, where calcium is tolerated at far higher levels.
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