The correct answer is: D. market portfolio
The required rate of return is the minimum rate of return that an investor expects to earn on an investment, given the level of risk involved. The market portfolio is a hypothetical portfolio that contains all of the assets in the market, in proportion to their market capitalization. The required rate of return for a stock in a portfolio is determined by the riskiness of the stock relative to the market portfolio. A stock that is more risky than the market portfolio will have a higher required rate of return, while a stock that is less risky than the market portfolio will have a lower required rate of return.
Option A, return portfolio, is incorrect because it does not specify the type of return that is being referred to. The required rate of return is a specific type of return, which is the minimum rate of return that an investor expects to earn on an investment.
Option B, in volatile portfolio, is incorrect because it does not specify the type of volatility that is being referred to. The required rate of return is a specific type of volatility, which is the riskiness of an investment.
Option C, volatile portfolio, is incorrect because it does not specify the type of portfolio that is being referred to. The required rate of return is a specific type of portfolio, which is the market portfolio.