For Number 2)
THE ELEMENTS TEND TO FORM COMPOUNDS BECAUSE AOMS ARE UNSTABLE AND CAN SHARE ELECTRONS IN THIER OUTER ENERGY LEVELS .
AS WE KNOW, ATOMS OF AN ELEMENT BECOMES MORE STABLE BY LOSING , GAINING AND SHARING ELECTRONS.
Elements react with each other to complete their octet or duplet so as to become stavle in nature. For e.g. Carbon reacts with oxygen to form carbon dioxide. Carbon reacts with four molecules of hydrogen to form methane - CH4.