The optimal combination of various sources of funds for a business is called:

Option 1 -> Capital structure refers to the specific mix of debt, equity, and other securities a company uses to finance its operations and assets.

Option 2 -> Financial planning is the broader process of managing finances, setting goals, and creating budgets, not specifically the mix of funding sources.

Option 3 -> Investment structure relates to how a company allocates its investments across different assets, not how it sources its funds.

Option 4 -> Stock structure refers only to the composition and classes of equity shares, which is just one component of total funding.

Hence, Option 1: Capital structure -> Capital structure specifically defines the optimal combination and proportion of various sources of funds (debt, equity, retained earnings, etc.) that a business uses to finance its operations and growth, making it the precise term for this concept -> correct