This nucleoside is cytidine. If the base were not bound to the sugar, this would be cytosine. If the 2' hydroxyl group were missing, this structure would be deoxycytidine. (The 2' hydroxyl is the  closest to the glycosidic bond between the base and the sugar). 

Nucleotides are formed by a pentose sugar (either ribose or deoxyribose), a nitrogenous base (adenine, cytosine, guanine, thymine, or uracil), and one or more phosphate groups. Polymers of nucleotides are known as nucleic acids (DNA and RNA).

The pyrimidines, which contain a single six-membered ring, are uracil, cytosine, and thymine. The purines, which contain a six-membered ring and a five-membered ring, are adenine and guanine. A mnemonic to help you remember these two groups is that pyrimidines, like pyramids are sharp - and sharp things CUT (cytosine, uracil, thymine).

Adenine and guanine are purines, while cytosine and thymine are pyrimidines.  A helpful mnemonic for this is Pure (purine) As (adenine) Gold (guanine).  Note that uracil is a pyrimidine, but is only seen in RNA.

The 80S eukaryotic ribosome is made up of 40S and 60S subunits.

The 70S prokaryotic ribosome is made up of 30S and 50S subunits.

IF-3 binds to the 30S subunit first. Then IF-2 forms the ternary complex, and it binds with IF-1 to the 30S subunit. Upon release of IF-1 and IF-3, the 50S subunit will bind to prepare for translation.

The nitrogenous bases that are considered to be pyrimidine derivatives are thymine, cytosine, and uracil. Thus, the purines are adenine and guanine. The mnemonic Pure As Gold (Purines = Adenine and Guanine) can be used to remember which bases are purines.

Nucleotides are monomers of nucleic acids and are made up of three molecules: nitrogenous base (uracil, thymine, cytosine, adenine or guanine), pentose sugar (deoxyribose for DNA and ribose for RNA) and phosphate group. Nucleosides, on the other hand, are molecules that only contain nitrogenous base and pentose sugar; they do not contain phosphate groups.

The question states that molecule A is heavier than molecule B. This could result from several reasons. First, molecule A could be a double stranded DNA and molecule B could be a single stranded RNA. This will allow the DNA molecule to be a lot heavier than its RNA counterpart. Second, molecule A could contain more purines (adenine and guanine) than molecule B). Recall that purines are two membered rings whereas pyrimidines (uracil, cytosine and thymine) are one membered rings. This means purines have more atoms and, therefore, have a higher molecular weight.

We are not given enough information to determine the identity or the distribution of nitrogenous bases in molecule A and B; therefore, we cannot conclude any of the given statements.