If there are 999 bases in an RNA that code for a protein with 333 amino acids, and the base at position 901 is deleted such that the coding length of the RNA becomes 998 bases, how many codons will be altered?

The correct option is B 33
In the given question, bases refer to the nitrogenous bases available in RNA- A, U, G, C.
A codon is in the form of a triplet of nitrogenous bases which code for one amino acid i.e., 3 bases (forming 1 codon) code for 1 amino acid. Similarly 999 bases(of sense codons) would code for 999/3=333 amino acids.
In the question, it has been given that the codon at position 901 was deleted. This means the previous 900 bases were intact and could code for 900/3=300 amino acids.
1 codon consists of 3 bases. Therefore, a deletion at the position 901 will affect the rest of the remaining 33 codons.