Question

chromosomes line up single file at the middle of the cell *
1 poin

prophase

metaphase

anaphase

telophase

Explanation:

To solve this, we recall the stages of mitosis:

• Prophase: Chromosomes condense, spindle forms, nuclear envelope breaks down. Not when they line up.
• Metaphase: Chromosomes align at the cell's equator (middle) in single file, attached to spindle fibers. This matches the description.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear envelope reforms.

So the correct stage is metaphase.

Answer:

B. metaphase