Testosterone, which is a steroidal hormone, has the following structure.
The total number of asymmetric carbon atom/s in testosterone is ____________.

Solution

Chemistry ma’am · 3 steps

Walk carbon by carbon and keep only the sp3 ones with four different groups around them.

1. Rule out first. A carbon in a C=O or C=C has only three groups, so it cannot be asymmetric. A CH₂ or CH₃ carbon has two identical H atoms, so it is out too.
2. Ring-junction carbons. Where two rings are fused, the carbon has its own group (H or CH₃) plus three ring bonds, and the paths around the rings are all different. Each such sp³ junction carbon is asymmetric. The one junction carbon in the C=C (C5) is sp², so it does not count.

   Carbon type (steroid numbering)	How many	Asymmetric?
   C=O and C=C carbons (C3, C4, C5)	3	no, sp²
   Ring CH₂ carbons (C1, C2, C6, C7, C11, C12, C15, C16)	8	no, two H atoms
   CH₃ carbons (C18, C19)	2	no
   sp³ ring-junction carbons: C10 and C13 (with CH₃), C8, C9, C14 (with H)	5	yes
   CH-OH carbon (C17)	1	yes: H, OH, C13 and C16 are all different

3. So. All 19 carbons are accounted for, and 5 + 1 = 6. Testosterone has 6 asymmetric carbon atoms.

The common slip: 7. Counting C5, the ring-junction carbon in the C=C double bond, gives 7. It is sp² with only three groups, so it cannot be asymmetric.

The idea to keep. In fused-ring molecules, every sp3 ring-junction carbon is a stereocentre. Count those, add any ring CH carrying a substituent, and skip anything sp2.

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