Final answer:
The risk measure for the volatility of an international portfolio is the standard deviation, which directly represents the volatility of an investment's returns.
Step-by-step explanation:
The risk measure for the volatility of an international portfolio is d. standard deviation. Each of the provided options represents a different statistical measure related to finance and investment risk. Alpha measures the performance of an investment relative to a benchmark index. Beta measures the volatility of an investment relative to the market as a whole. The Sharpe ratio measures the performance of an investment compared to a risk-free asset, after adjusting for its risk. However, standard deviation is the statistical measure that directly represents the volatility of an investment's returns, which is crucial for gauging the risk of an international portfolio.