The element which has the maximum number of valence electrons is:

An element which is an essential constituent of all organic compouds belongs to following group of modern periodic table:

Which of the following is the valence shell for the elements of second period of the modern periodic table?

The correct increasing order of the atomic radii of the elements oxygen, fluorine and nitrogen is:

The atomic numbers of the elements Na, Mg, K and Ca are 11, 12, 19 and 20 respectively. The elements having the largest atomic radius is: