Pls help me 1:__Cu20 + ___C ↠__Cu + ___CO2

2:___ Na + ___O2 ↠ ___ Na2O
3:___ C2H4 + ___ O2 → ___ CO2 + ___ H2O
4:___ C4H10O + ___ O2 ↠ ___ CO2 + ___ H2O

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation:

answer; the above answer to the above statement is (true)

the correct answer to this question is #5