Which feature is used to classify galaxies? age, color ,shape, size wich one need asap

The correct answer is Shape.

Explanation:

Galaxies are defined as the system of million or billions of stars along with gas and dust held together by gravitational attraction.

These are classified as 3 types on the basis of its shape:

1. Spiral galaxy: It is defined as the galaxy in which stars and gas clouds are located mainly in one or more spiral arms. Example: Milky Way

2. Elliptical galaxy: It is defined as the galaxy which has ellipsoidal shape and a smooth, featureless image. Example: M-110.

3. Irregular galaxy: It is defined as the galaxy that does not have any distinct regular shape. Example: Irr-I galaxy.

Hence, the correct answer is Shape.