Answer: 2. Disk
Explanation:
Stars, gas and dust are closely packed at the center in Bulge. A Bulge is present at the heart of most of the Spiral galaxies. Bulge has a flattened sphere i.e. a disk like shape.
This disk has high compact mass at its center which is assumed to be a super-massive black-hole. All the material in the disk rotates about this black-hole.
Thus, the correct answer is a flattened combination of matter containing stars, gas, and dust in spiral galaxy can be identified as 2. Disk
A galaxy is a group of stars, gas and dust. Spiral galaxy and elliptical galaxy are types of galaxy. Gravitational force binds the all the material in the galaxy.