Spot the correct spelling of an electron-transport protein.

The correct option is Cytochrome.

Explanation:

A cytochrome is a type of iron-containing heme protein involved in electron transport chains within cells, essential for processes such as cellular respiration and photosynthesis.

Let's analyze the spelling options provided:

1. Cytocrhome - Incorrect (misplacement of the letter 'r').
2. Cytocrom - Incorrect (missing the 'h' and final 'e').
3. Cytochrome - Correct (derived from Greek kytos meaning "container/cell" and chroma meaning "color").
4. Cytohrom - Incorrect (missing the letter 'c').

Therefore, the correctly spelled term for the electron-transport protein is Cytochrome.