Which condition in a nebula would prevent nuclear fusion

A decrease in the overall volume of gases like hydrogen can prevent nuclear fusion in a nebula.

Explanation:

Nuclear fusion: The reaction of combining two or more atomic nuclei to form one or more different atomic nuclei and subatomic particles is known as nuclear fusion. A single heavy nucleus is formed from two lighter nuclei. Helium is made by fusing Hydrogen atoms together.

Nebula: A nebula is a giant cloud dust and gas in space. Nebulae are formed out of the gas and dust that are thrown out by the explosion of a dying star.

A decrease in the overall volume of gases like hydrogen can prevent nuclear fusion in a nebula.