Which of the following is not a true statement? 0.2 moles O 2 = 6 g
0.75 moles H 2CO 3 = 47 g
3.42 moles CO = 84.0 g

3.42 moles CO = 84.0g, is not true.

Explanation:

Moles is given by the formular; Mass / Molar Mass.

Therefore; 0.2 moles O2 = 6g is true  when we multiply 32g x 0.2 = 6g approximately.

 0.75 moles H2CO3 = 47g.

Molar formular for H2CO3 = 2 + 12 + 48 =62g.

If we multiply  62g (molar mass ) by 0.75moles, it gives us 47g approximately.

3.42 moles CO = 84g

molar mass of CO = 12 + 16 = 28g

Multiply 28g x 3.42 moles =  95.76g, which is not true.