Amale fish releases sperm cells into the water. one of the sperm cells unites with an egg from a female fish to form a new cell that grows into the new fish. is it asexual or sexual reproduction?

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?