What occurs when sodium reacts with water?

When sodium reacts with water, a highly vigorous reaction takes place, producing sodium hydroxide and hydrogen gas. The reaction begins with the release of hydrogen gas, which is observed as fizzing or bubbling on the surface of the sodium. This fizzing occurs because the hydrogen gas escapes from the liquid, and it is a clear visual indication of the reaction taking place.

In addition to fizzing, sodium is less dense than water, which means it floats on the surface. As the sodium continues to react with water, the released heat can ignite the hydrogen gas, sometimes resulting in a small flame. This further emphasizes the vigorous nature of the reaction.

While the other options mention sinking, gas production, and discoloration, the prominent observable effect during the initial phase of sodium's reaction with water is indeed the fizzing caused by the hydrogen gas bubbles. The visual cue of fizzing is a direct consequence of the production and escape of the gas, making it the most characteristic feature of the reaction.