Mitosis stage identified by chromosome alignment at equator without nuclear envelope

Steps:

• Recall mitosis stages: prophase (chromosome condensation, nuclear envelope breakdown), metaphase (alignment at equator), anaphase (separation to poles), telophase (reformation at poles).
• Note absence of nuclear envelope: occurs after prophase, ruling out telophase.
• Observe chromosomes lined up at cell equator: defines metaphase plate formation.
• Confirm no separation to poles: excludes anaphase.

Why B is correct:

• Metaphase features chromosomes aligned singly at the equatorial metaphase plate following nuclear envelope disassembly.

Why the others are wrong:

• A: Prophase shows condensing chromosomes not yet aligned at equator.
• C: Anaphase displays chromosomes pulled apart toward opposite poles.
• D: Telophase involves decondensed chromosomes at poles with reforming nuclear envelope.

Final answer: B