What change inside Earth does the Lehmann discontinuity represent?

Correct answer: Transition from outer core to inner core

The Lehmann discontinuity is the boundary between Earth’s liquid outer core and solid inner core. It shows a major change in material and physical state inside the core. Seismic waves behave differently when they pass across this boundary, which helps scientists identify it. Therefore, the transition from the outer core to the inner core, given in option A, is correct. The crust–mantle boundary is called the Mohorovičić or Moho discontinuity, so option B describes a different boundary. The remaining choices concern unrelated parts of Earth or its atmosphere.

Earth is commonly described as having the crust, mantle, outer core and inner core. The Lehmann discontinuity occurs deep within the core, not near the surface. The outer core is mainly liquid, whereas the inner core is solid because of the enormous pressure at the centre. Thus, when the question asks what change the Lehmann discontinuity represents, the correct reasoning is to identify the core boundary. Hence, option A is the appropriate answer.