Final answer:
Advocacy advertising is used to safeguard against negative consumer attitudes and enhance credibility among supporters, differing from product, pioneering, and competitive advertising. The correct option is (a).
Step-by-step explanation:
The form of institutional advertising typically used to protect against negative consumer attitudes and to enhance a company's credibility among consumers who already favor the company's position is called advocacy advertising.
Advocacy advertising is focused on promoting a company's views on certain issues or responding to media controversy, rather than promoting a product itself.
As opposed to product advertising, which highlights the attributes of a specific product, or pioneering advertising and competitive advertising, which are aimed at establishing a market presence and outshining competitors respectively, advocacy advertising plays a role in shaping public perception and maintaining a positive reputation.