Why are some amino acids described as essential amino acids?
a) they are the ones most used in the body.
b) they can be stored in the body.
c) they are the only ones needed by the body.
d) they cannot be made by the body.

Option (D) is the correct answer.

Explanation:

Organic compounds which are simple and contains carboxylic acid group (COOH) and amino group are known as amino acids.

Amino acids which are synthesized by the human body are known as non-essential amino acids.

For example, alanine, aspartic acid etc are non-essential amono acids.

Whereas amino acids which are not synthesized by human body are known as essential amino acids.

For example, arginine, histidine, isoleucine etc are all essential amino acids.

Therefore, we can conclude that some amino acids described as essential amino acids because they cannot be made by the body.

they are both synthetic elements

explanation:

d

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.