The atomic numbers of elements A, B, C and D are 2, 6, 12 and 20 respectively. Which of them has 2 electrons in its N shell?

1. A
2. D
3. B
4. C

The number of atoms in a chloride ion is:

1. One
2. Two
3. Three
4. Four

When an oxygen ion is converted to an oxygen atom, it undergoes:

1. Reduction
2. Redox reaction
3. Oxidation
4. Combination reaction

The element whose atomic weight was corrected on the basis of its position in Mendeleev's periodic table is :

1. Hydrogen
2. Gold
3. Silver
4. Copper