closed as off-topic by Mithoron, airhuff, aventurin, Tyberius, Todd Minehardt Jun 5 '18 at 23:07
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Homework questions must demonstrate some effort to understand the underlying concepts. For help asking a good homework question, see: How do I ask homework questions on Chemistry Stack Exchange?" – Mithoron, aventurin, Tyberius, Todd Minehardt
If you look at the question closely, it states in the equation, moles per litre. The reason the moles are divided by two is the fact you need to find the moles of CO2 in 500 ml and not 1000 ml.