Question

Under a light microscope, a stained cell shows chromosomes lined up along the middle. What will happen next?

Answer 1

This question's talking about Mitosis.

You know the four stages of mitosis?

Prophase, Metaphase, Anaphase, and Telophase.

The question is talking about the part of mitosis where the chromosomes are "lined up along the middle."

Take a look at this picture:
http://edgefile.net/wp-includes/Text/Diff/mitosis-phases-diagram-i6.gif

Do you see how in METAPHASE, the chromosomes are lined up in the middle?

That means that the question is describing Metaphase.

But the REAL question is "What will happen next?"

Take a look at the next step, after Metaphase: ANAPHASE.

After Metaphase, and during Anaphase,
the spindles (little strings) attach to the centromeres (centers) of the chromosomes,
and the chromosomes are pulled apart.

That is what happens next, during Anaphase.
You see there, in the picture?