Aluminous shell that surrounds some hot stars is called a
a. red giant
b. protostar
c. supernova
d. planetary nebula

The correct answer is option D.

Explanation:

Red giant is defined a star with large size, volume and low surface temperature.They are luminous giant star with size relatively larger than that of the sun along with the reddish hue.

Protostar is defined as early stage in formation of star which is still in the process of gathering mass from its parent molecular cloud.

Supernova is defined as star in which its brightness suddenly increases and further leads to the explosion with release of very large amount of energy.

Planetary nebula is defined as star consisting of glowing shell formed of gas and plasma which are formed by the dying star.

frequency or wavelenth of em radiation in a vacuum