Three elements A, B and C have atomic number 7,8 and 9 respectively.
(a) What would be their positions in the modem periodic table (Mention group and period both).
(b) Arrange A, B and C in the decreasing order of their size.
© Which one of the three elements is most reactive and why ?
(a) Position of A = 15th group, 2nd period
Position of B = 16th group, 2nd period
Position of C = 17th group, 2nd period
© C is most reactive as it has smallest size, so it can easily gain electrons.