gnus-confirm-mail-reply-to-news

gnus-confirm-mail-reply-to-news is a variable defined in `gnus-msg.el'.
Its value is

t

Documentation:
If non-nil, Gnus requests confirmation when replying to news.
This is done because new users often reply by mistake when reading
news.
This can also be a function receiving the group name as the only
parameter, which should return non-nil if a confirmation is needed; or
a regexp, in which case a confirmation is asked for if the group name
matches the regexp.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.