JEE Main levelSingle correct optionDifficulty 2 of 3pl205
A 100 g sample of natural rubber (repeat unit CX5HX8, 68 g/mol) is vulcanised with 3.2 g of sulfur (S = 32). Assume all the sulfur is present as single S atoms, each bridging exactly two different isoprene units, and no unit takes part in more than one bridge. The percentage of isoprene units involved in cross-links, correct to one decimal place, is
A6.8
B27.2
C3.2
D13.6
Answer: D
Moles of S = 3.2/32 = 0.10, giving 0.10 mol of bridges and 0.20 mol of cross-linked units. Isoprene units = 100/68 = 1.4706 mol. Percentage = 0.20/1.4706 x 100 = 13.6.