Ответ:

Mr(Ca₃N₂) = 40*3+14*2 = 148

Mr(Cr(OH)₃) = 52+ 17*3 = 103

Mr(H₂CO₃) = 1*2+12+16*3 = 62

w(H) = 2/62= 3,23%

w(C) = 12/62 = 19,35%

w(O) = 48/62 = 77,42%