$XeF_2$ reacts with $SbF_5$ to form

Among the fluorides below,the one which does not exist is

Argon was discovered by

What are the elements at the end of periods $1$ to $7$ called? Which are these elements?

The density of nitrogen prepared from air is slightly higher than that of nitrogen prepared from chemical compounds. This is due to the presence of which of the following in nitrogen obtained from air?

Which is the last element of the noble gas group?