Option 1 states that both statements are true and that Statement II is the correct explanation of Statement I. Let`s analyze each statement to understand if this is the correct answer.

Statement I states that diamond is very hard and has a high melting point. This statement is true. Diamond is formed from carbon atoms that are each covalently bonded to four other carbon atoms, creating a strong, rigid network structure. This arrangement of carbon atoms leads to the hardness and high melting point of diamond.

Statement II states that in diamond, each carbon atom is covalently bonded to four other carbon atoms to form a three-dimensional network. This statement is also true. The arrangement of the carbon atoms in diamond creates a strong covalent bond network, where each carbon atom is bonded to four neighboring carbon atoms. This extensive bonding forms a three-dimensional lattice structure, resulting in the unique properties of diamond.

Therefore, Statement II provides a correct explanation for Statement I. The strong covalent bonding in diamond, created by each carbon atom being bonded to four other carbon atoms, is the reason for its hardness and high melting point. Hence, option 1 is the correct answer.