1. Over three years, Marina did not invest funds from her Individual Investment Account (IIS) into financial instruments and therefore did not receive any income from the IIS. However, she still acquired the right to an investment tax deduction for contributing personal funds to the IIS (Article 291.1 of the Tax Code of the Russian Federation).

The tax deduction is provided in the amount of funds deposited in the tax period into the IIS, but not exceeding 400,000 rubles in total per year.

Marina is entitled to receive 13% of the amount deposited into the IIS from the state in the form of a refunded personal income tax (NDFL) that she paid to the treasury from her income.

The amount of NDFL deducted from Marina's annual salary = 30000 * 12 months * 0.13 = 46800 rubles.

The tax deduction for the first year = 100000 * 0.13 = 13000 rubles. This amount does not exceed the amount of NDFL deducted from Marina's annual salary.

The tax deduction for the second year = 400000 * 0.13 = 52000 rubles. This amount exceeds the amount of NDFL deducted from Marina's annual salary. Therefore, the tax deduction will be limited to the amount of NDFL paid for the second year of the IIS's existence, or 46800 rubles.

The tax deduction for the third year = 400000 * 0.13 = 52000 rubles. This amount also exceeds the amount of NDFL deducted from Marina's annual salary. Therefore, the tax deduction will be limited to the amount of NDFL paid for the third year, or 46800 rubles.

The total tax deduction over 3 years = 13000 + 46800 + 46800 = 106600 rubles.

The return on Marina's operations over 3 years = 106600 / 1000000 * 100% = 10.66%.

The annual return on Marina's operations = 10.66% / 3 = 3.55%.
Answer: $\mathbf{3 , 5 5 \%}$