[18]-crown-6 has:

A) 18 Carbon & 6 Oxygen atoms
B) 6 Carbon & 18 Oxygen atoms
C) 12 Carbon & 6 Oxygen atoms
D) 6 Carbon & 12 Oxygen atoms

Key

Crown ether named [T]-crown-O, means T is the total number of atoms in the ring and O is the number of oxygen atoms in the ring.

For, [18]-crown-6 there are 6 Oxygen atoms and a total of 18 atoms.

So, number of Carbon atoms = 18 – 6 = 12

Hence, option (C).