Consider the following statements with reference to the periodic table of chemical elements.
1. Ionization potential gradually decreases along a period.
2. In a group of elements, electron affinity decreases as the atomic weight increases.
3. In a given period, electronegativity decreases as the atomic number increases.
Which of these statement(s) is/are correct?

The chemical composition of diamond is

Consider the following statements with reference to the periodic table of chemical elements.
1. Ionization potential gradually decreases along a period.
2. In a group of elements, electron affinity decreases as the atomic weight increases.
3. In a given period, electronegativity decreases as the atomic number increases.
Which of these statement(s) is/are correct?

Approximately, how many different chemical elements exist in the Earth?

Which is the most abundant element after oxygen?