`underset(2xx12=24g)(2C)+underset(32g)(O_(2))rarrunderset(2xx28=56g)(2CO)`
24 g of C will require oxygen `(O_(2)) = 32 g`
But `O_(2)` actually available = 96 g
(a) Therefore, reactant left in excess `= O_(2)`
(b) Mass of `O_(2)` left unreacted `= 96 - 32 = 64 g`
(c) For reacting with 32 g of `O_(2)`, carbon needed = 24 g
For reacting with 96 g of `O_(2)`, carbon needed `= ((24g))/((32g))xx(96g)=72g`.