The answer is leucine would be in the interior, and serine would be on the exterior of the globular protein.
The side chain (R group) of the amino acid serine is CH₂OH. The side chain of the amino acid leucine is CH₂CH(CH₃)₂. In globular protein, leucine found in the interior, and serine found on the exterior. The nature of side chain decides the amino acid position in the globular protein , as CH₂CH(CH₃)₂ this is hydrophobic and CH₂OH is hydrophlic.