Ответ:

С3H8 =  44 

Cu2S = 160

NH3 = 17

MgO = 40

Ответ:

M(C3H8) = 44; C = 12 * 3 / 44 * 100% = 82% ; H =  1 * 8 / 44 * 100% = 18%

M(Cu2S) = 160; Cu = 64 * 2 /160  * 100% = 80% ; S = 32 * 1 / 160 * 100% = 20%

M(NH3) = 17; N = 14 * 1 /17  * 100% = 82% ; H = 1 * 3 / 17 * 100% = 18%

M(MgO) = 40; Mg = 24 * 1 /40  * 100% = 60% ; O = 16 * 1 / 40 * 100% = 40%

 

В некоторых случаях массовая доля примерна