How are elliptical galaxies different from spiral galaxies? a. They contain older stars and less gas and dust.
b. They contain younger stars and more gas and dust.
c. They are bigger than spiral galaxies.
d. They are smaller than spiral galaxies.

A. They contain older stars and less gas and dust.

Explanation:

There are three types of galaxies:

Elliptical galaxies are galaxies shaped like an ellipse, while spiral galaxies consist of a flat, rotating disk that contains stars, gas, and dust, and a central concentration of stars called the bulge.

The difference between elliptical and spiral galaxies is in the amount of gas and dust they contain. Spiral galaxies contain large amounts of gas and dust, which means that new stars are born very often. This makes them brighter than relatively dim elliptical galaxies, which contain less gas and dust. This is why fewer new and brighter stars are born in elliptical galaxies, leaving them with older, dimmer stars.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.