Assertion (A): The outer core of the earth's interior is in molten state while the inner core is in solid state. Reason (R): The P-seismic waves disappear in outer core while S-waves penetrate up to the inner core.

Correct Answer: (A) is true but (R) is false. The Earth was discovered to have a solid inner core distinct from its liquid outer core in 1936, by the seismologist Inge Lehmann, who deduced its presence by studying seismograms from earthquakes in New Zealand; she observed that the seismic waves reflect off the boundary of the inner core and can be detected by sensitive seismographs on the Earth's surface. Typical values for P-wave velocity in earthquakes are in the range 5 to 8 km/s. The precise speed varies according to the region of the Earth's interior, from less than 6 km/s in the Earth's crust to 13 km/s through the core.