Main source of helium is
(a) air
(b)radium
(c) monazite
(d)water
Main source of helium is
(a) air
(b)radium
(c) monazite
(d)water

Correct option is C

Monazite is a phosphate mineral [(Ce, La, Nd, Th)PO4], the major commercial source of Ce. Occurring as small heavy crystals in granitic and gneissic rocks and their detritus (called monazite sands), monazite contains up to 27 wt. From: An Introduction to Nuclear Waste Immobilisation, 2005