The elements of a period of the periodic table are given in order from left to right with one of its element missing:
a. To which period do these elements belong?
b. One element of this period is missing. Which is the missing element and where should it be placed?
c. Which one of these elements in this period shows the property of catenation?
d. Which one of these elements is least reactive?
(a) Na11 = 2, 8, 1
Since all elements have 3 shells so these elements belong 3rd period.
(b) The missing element is phosphorus (P) which has 15 atomic number. So it should be placed between Si and S.
(c) Si shows the property of catenation because it has 4 valence electrons so it forms long chain.
(d) We know that noble gases are less reactive due to complete octet. So Ar is less reactive because Ar is a noble gas.