Based on the options provided, the question that can be placed in the property column instead of the letter X should relate to a property that distinguishes electromagnetic and mechanical waves.
Among the options, "How does this wave transfer matter?" is the most suitable replacement for X, since it addresses the fundamental characteristics of wave types: mechanical waves transfer matter (they propagate through a medium), while electromagnetic waves do not require a medium to travel.
So, the answer to replace letter X would be:
How does this wave transfer matter?