0.1 mol of the following given antiviral compound (P) will weigh ________ × 10⁻¹ g (nearest integer).
(Given : molar mass in gmol⁻¹H:1,C:12, N:14,O:16, F:19,I:127 )

Solution

Chemistry ma’am · 3 steps

Count every atom in the structure, including the hidden H on each carbon, then add up the molar mass.

1. Count the atoms. The sugar ring has 5 C and the uracil ring has 4 C, so 9 C in all. The H atoms are 4 ring CH, 1 CH₂ (2 H), 2 OH and 1 NH, plus 1 ring =CH, which makes 10 H. The O atoms are the ring O, 2 OH and 2 C=O, so 5 O.

   Element	Number of atoms	Mass (g mol⁻¹)
   C	9	9 × 12 = 108
   H	10	10 × 1 = 10
   N	2	2 × 14 = 28
   O	5	5 × 16 = 80
   F	1	19
   I	1	127
   Total	C₉H₁₀FIN₂O₅	372

2. Mass of 0.1 mol. Mass = 0.1 × 372 = 37.2 g. Written in the form asked, that is 372 × 10⁻¹ g.
3. So. The blank is 372.

The common slip: 37. Writing the mass in grams, 37.2 g, and rounding it gives 37. The question asks for the number multiplying 10⁻¹, which is 372.

The idea to keep. In a skeletal structure every carbon carries enough H to make four bonds. Count those hidden H atoms, write the full molecular formula, then add the masses.

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