chemisty help please!?

Question

Which of the following ions occurs commonly?
N3+
S6+
O2-
Ca+
Cl+

2. Sodium hydroxide, also known as caustic soda, is used to neutralize acids and to treat cellulose in making of cellophane. Calculate the number of moles of solute in 1.875 L of 1.356 M NaOH solution.
2.543 mol
1.383 mol
0.7232 mol
0.3932 mol
0.001383 mol

3. How many mL of concentrated nitric acid (HNO3, 16.0 M) should be diluted with water in order to make 2.00 L of 2.00 M solution?
32.0 mL
62.5 mL
125 mL
250. mL
500. mL

Answer 1

1) O(2-)
2) 2.543 mol
3) 250. mL