The correct answer is: A. Before Tax basis
The cost of capital for bonds and debentures is calculated on a before-tax basis because the interest payments on these securities are tax-deductible for the issuer. This means that the after-tax cost of debt financing is lower than the before-tax cost.
The risk-free rate of interest is the rate of return that an investor would expect to earn on a security that is free of default risk. This rate is used as a benchmark for the cost of debt financing, but it does not take into account the tax deductibility of interest payments.
Option B is incorrect because the cost of debt financing is calculated on a before-tax basis. Option C is incorrect because the risk-free rate of interest does not take into account the tax deductibility of interest payments. Option D is incorrect because the cost of capital for bonds and debentures is calculated on a before-tax basis.