(a) The activities of a corporation affect all the residents of the corporation's authorizing unit by the corporation's assuming to a material extent what otherwise might be an obligation or duty of the authorizing unit, and therefore the corporation is an institution of purely public charity within the tax exemption of Section 2, Article VIII, Texas Constitution.
(b) A corporation is exempt from the tax imposed by Chapter 171, Tax Code, only if the corporation is exempted by that chapter.