In mitosis, chromosome duplication occurs during

The correct option is B Interphase
The cell cycle has three phases that must occur before mitosis. The three phases are collectively known as INTERPHASE.

They are $G_1,S\&G_2$. The $G$ stands for gap & $S$ stands for synthesis. The $G_1$ & $G_2$ phase are times of growth & preparation for major changes. The synthesis phase is when the cell duplicates the DNA in its genome.

Synthesis Phase:-

During the synthesis phase, a cell copies its DNA. DNA replication is a massive effort that requires a lot of proteins. Since DNA does not exit by itself in a cell but is packaged by proteins, more packaging proteins must also be made during the $S$ phase. Histones are proteins around which DNA wraps. The production of new histone proteins starts at the same time as DNA synthesis.

In mitosis, chromosome duplication occurs during interphase.