Compounds of Group 17

The colour of the X_(2) molecules of group 17 elements changes gradually from yellow to violet down the group. This is due to

Which of the elements of group 17 is radioactive ?

Why are the elements of group 17 generally coloured ?

The number of np-electrons in the outer shell of elements of group 17 is

which of the following element of Group 17 shows radio-activity?