Choose the answer that best explains why Orion is important to star watchers. Orion is located on the celestial equator. Its location causes the rest of the stars to appear to revolve around Orion as the Earth rotates.
Since Orion can be seen in both the Southern and Northern Hemispheres it is useful for finding north in the night sky.
Orion, the hunter, was an important figure in Greek Mythology making the constellation of central importance to astronomers.
Orion is easy to locate, it can be seen in both hemispheres and is helpful for locating prominent stars, nebulas and surrounding constellations.

Orion is located on the celestial equator. Its location causes the rest of the stars to appear to revolve around Orion as the Earth rotates.

Explanation:

The above stated statement is the reason why those who watches for stars commonly called the star watchers use the Orion as their base point in star observation. Without this, it would be difficult to trace the stars or know the exact ones which appears on the sky.

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.