Gold

so the difference is in carats (carat is a unit used for mass/purity of gold and other gems),

u bought 22 carat jewellery,
and according to your mother in law 22 carat is no good, 24 carat would have been better (in her view more carats more gold)...

but that doesn't mean she's right in her view... as others have pointed out 24 carat gold tends to be too soft/meallable for jewellery...depending on the design, if you got 24 carat karas or chooriyan, they would be more prone to dents...
almost all jewellery that is made and sold now a days is with 22 carat gold alloy, not 24 (as 24 has problems with dents , breakage etc)

your mother in law is wrong :) , you can tell her that in a nice manner , that for the stuff you bought bai ka sona hi acha hei :P
or if you dont want o say anything to her then dont , but know for yourself that the stuff u bought is perfectly fine...