Naphthalene, $C X_{10} H X_{8}$ , has two fused six-membered carbon rings. Counting each bond's sigma component once, find the total number of sigma bonds (C-C and C-H) in one molecule (give an integer).

Numerical answer type, tolerance 0.5.

Answer: 19

Naphthalene has 10 + 8 = 18 atoms and 2 rings. Sigma bonds = atoms - 1 + rings = 18 - 1 + 2 = 19. Check: 11 C-C sigma bonds + 8 C-H bonds = 19.