No corporate income or franchise tax shall be imposed upon:

A. insurance companies, reciprocal or inter-insurance exchanges which pay a premium tax to the state;

B. a trust organized or created in the United States and forming part of a stock bonus, pension or profit-sharing plan of an employer for the exclusive benefit of his employees or their beneficiaries, which trust is exempt from taxation under the provisions of the Internal Revenue Code; or

C. religious, educational, benevolent or other organizations not organized for profit which are exempt from income taxation under the Internal Revenue Code unless the organization receives income which is subject to federal income taxation as “unrelated business income” under the Internal Revenue Code, in which case the organization is subject to the corporate franchise tax, and the corporate income tax applies to the unrelated business income.