Which of the following elements will form an acidic oxide?
A. An element with atomic number 7

B. An element with atomic number 3

C. An element with atomic number 12

D. An element with atomic number 19

Account for the following:

a. Cations are smaller in size than the corresponding atom.

b. The noble gases were discovered very late.

Why are isotopes of an element having different atomic masses placed at the same position in the periodic Table?

The electronic configuration of four elements A,B,C and D is given as follows:

A-2,8 B-2,8,1

C-2,8,2 D-2,8,8

a. Which of them belong to the same period? Name the period.

b. Which of them belong to the same group? Name the group.

Na, Mg and Al are the elements of the 3rd period of the Modern periodic Table having group number 1,2 and 13 respectively. Which one of these elements has the (i) highest valency, (ii) largest atomic radius, and (iii) maximum chemical reactivity? Justify your answer stating the reason for each.

OR

Based on the group valency of elements, state the formula for the following giving justification for each:

i. Oxides of group 1 elements

ii. Halides of the elements of group 13 and

iii. Compounds formed when an element of group 2 combines with an element of group 16.

Name the elements which has:

(i) a total of three shells with three electron in its valence shells.

(ii) Half as many electronic in its third shell as in its second shell.

Arrange the following elements in the increasing order of their atomic radii.

Li, Be, N and F

Upto which element the law of octaves was found to be applicable?