Fixed-interest investments expose the investor primarily to purchasing power risk, also called inflation risk. When an investment pays a fixed rate, the nominal payment does not automatically rise with inflation. If the cost of goods and services increases faster than the fixed return, the investor’s real return declines. For example, a bond paying 4% may appear stable, but if inflation rises to 6%, the investor loses purchasing power even though the issuer continues paying interest. Credit risk is the risk that an issuer cannot meet its payment obligations; it may apply to some bonds but is not the central risk described by fixed interest payments. Political risk concerns changes in government policy or instability. Liquidity risk concerns the ability to sell without significantly affecting price. The question focuses on the erosion of fixed payments over time, making purchasing power risk the best answer. The SIE outline lists “Inflationary/purchasing power” as a core investment risk and also identifies debt instruments as products that generate income through interest. Reference: Section 2.1.2 Debt Instruments; Section 2.2 Investment Risks.