What does the (lll) in iron ion mean

What is the result of multiplying (2.5 × 1010) × (2.0 × 10-7)? a. 5.0 × 103 b. 5.0 × 10-3 c. 5.0 × 1017 d. 5.0 × 10-17

Why does his teacher ask him to balance the equation by including the correct coefficient

Joan writes four numbers on the board in standard form, and then she writes their scientific notation