Correct Answer - Option 2 : C
Number of naturalist want to see only bat is 100 - (15 + 30 +10 + 20 + 5)
⇒ 20
Number of naturalists who wants to see only butterfly is 15
Required ratio is 20 : 15
⇒ 4 : 3
∴ The ratio of naturalists who want to see only bats is to those who want to see only butterflies is 4 : 3