When 3 g of magnesium nitrate is added to water a solution of 100 cm 2 is formed what is the concentrated of ions in the solution?

Molar mass of Mg(NO₃)₂ = (24.31 + 14.01×2 + 16.00×6) g/mol = 148.33 g/mol
No. of moles of Mg(NO₃)₂ = mass / moles = (3g) / (148.33 g/mol) = 0.0202 mol

Volume of the solution = 100 cm³ = 0.1 dm³

Concentration of Mg(NO₃)₂ = moles / volume = (0.0202 mol) / (0.1 dm³) = 0.202 M

1 mole of Mg(NO₃)₂ contains 3 moles of ions (1 mole of Mg²⁺ ions and 2 moles of NO₃⁻ ions).
Concentration of ions = (0.202 M) × 3 = 0.606 M ≈ 0.61 M

...... The answer is : B. 0.61 M