Does the ability to untap all permanents during an opponent's untap step qualify as a lapsing ability?

The correct understanding stems from the nature of the ability being discussed. An ability that allows a player to untap all permanents during an opponent's untap step is classified as a lapsing ability because it affects the game state during a specific phase that is not under the controlling player's direct control—namely, the opponent's untap step.

Lapsing abilities are defined as those that occur or can occur without requiring an additional choice from the player controlling the ability at the time it happens. In this case, since the ability activates at the specified time (the opponent's untap step) and results in multiple permanents being untapped, it fits the criteria of a lapsing ability. The fact that it is capable of impacting multiple permanents reinforces this classification, as lapsing abilities typically encompass effects that have broader implications on the game state.

This understanding illustrates the distinction between passive abilities that automatically trigger in accordance with game timing and more interactive abilities that require player input or decision-making outside of their designated timing.

The reasoning for why this option is the best answer emphasizes the nature of game mechanics and how actions unfold in relation to turn structure and player agency within those phases.