$${\textbf{Step 1}}\;:\;{\mathbf{Finding}}\;{\mathbf{number}}\;{\mathbf{of}}\;{\mathbf{words}}\;{\mathbf{starting}}\;{\mathbf{with}}\;{\mathbf{the}}\;{\mathbf{alphabets}}\;{\mathbf{in}}\;{\mathbf{the}}\;{\mathbf{given}}\;{\mathbf{word}}$$
$${\text{No}}.{\text{ of words beginning with A }}
= 4! = 4 \times 3 \times 2 = 24$$
$${\text{No}}.{\text{ of words beginning with N }}
= 4! = 4 \times 3 \times 2 = 24$$
$${\text{No}}.{\text{ of words beginning with R }}
= 4! = 4 \times 3 \times 2 = 24$$
$${\text{No}}.{\text{ of words beginning with U }}
= 4! = 4 \times 3 \times 2 = 24$$
$${\text{So}},{\text{ in total }}96{\text{ words will be formed while beginning with letter A}},{\text{ N}},{\text{ R and U}}.$$
$${\textbf{Step 2}}\;\;:\;{\mathbf{Finding}}\;{\mathbf{the}}\;{\mathbf{order}}\;{\mathbf{of}}\;{\mathbf{the}}\;{\mathbf{word}}$$
$${\text{Order of }} 97{\text { th word }}
- {\text{ VANRU}}$$
$${\text{Order of }}98{\text{th word }}
- {\text{ VANUR}}$$
$${\text{Order of }}99{\text{th word }}
- {\text{ VARNU}}$$
$${\text{Order of }}100{\text{th word}}
- {\text{ VARUN}}.$$
$${\mathbf{Therefore}},\;{\mathbf{rank}}\;{\mathbf{of}}\;{\mathbf{word}}\;'{\mathbf{VARUN}}'\;{\textbf{is 100. Option C is correct.}}$$