Which of the following groups of elements are included in the main group of elements?

Alkali metals 
Nonmetals
Halogens

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.