Which one of the following is present in the largest amount in terms of percent by mass in the Earth's crust?

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?