a) 8%–9%
b) 5%–8%
c) 2%–5%
d) 1%–2%

Answer: c
Explanation: The residual lignin content in chemical pulp accounts for 2%–5% of the mass. It is responsible for the dark color of the unbleached pulp. The reagents for full bleaching of chemical pulp are mostly oxidative and since the carbohydrates are also susceptible to oxidation, bleaching must be accomplished under the mildest conditions.