Question

Frequency analysis can be performed on polyalphabetic ciphers which makes it weaker than monoalphabetic ciphers

Answer 1

Multiple cipher alphabets are required  to increase security.

Crypt analysis  are made harder with more alphabets.Each alphabet is used in turn.When end of key is searched it is then repeated from start.

In mono alphabetic what happens is that there is a fixed substitution but poly alphabetic  cipher uses multiple substitution therefore frequency analysis when performed poly alphabetic ciphers makes it weaker.

Answer 2

what do mono alphabetic  do  is that there is a fixed substitution but poly alphabetic  cipher uses multiple substitution therefore frequency analysis when performed poly alphabetic ciphers makes it weaker.Multiple cipher alphabets are required  to increase security.Crypt analysis  are made harder with more alphabets.Each alphabet is used in turn.When end of key is searched it is then repeated from start.