a) 1%–2%
b) 3%–5%
c) 2%–3%
d) 4%–6%

Answer: d
Explanation: The soda process consisted of boiling wood in 4%–6% sodium hydroxide liquor at a high temperature (170°C). This process is now obsolete. Less than 2% of the pulp produced today uses this process which is very similar to the sulfate process, except that only sodium hydroxide is used. Essentially all former soda mills have converted to the sulfate process.