The correct option is A boldness
Timidity means lack of courage or confidence. The opposite of timidity is boldness, or willingness to take risks and act innovatively. Hence, Option A is correct. Among the rest of the options, arrogance means haughtiness, self-assertion means the confident and forceful expression or promotion of oneself, one's views, or one's desires, self-confidence means a feeling of trust in one's abilities, qualities, and judgement. These do not express this antonym, hence incorrect.