How IR spectroscopy works 

And hence co2 is Raman active

Wrong

Symmertic CO2 is IR inactive, most symmetric molecules like Symmetric and Psudosymmetric Alkenes and Alkynes are IR inactive cause symmetry indicates no net electrical diapole. It is a must condition for a molecule to be IR active is to have some diapole. In case of CO2, it shows two stretching frequencies; 1. Symmetric stretch (no net diapole) hence IR inactive and 2. Asymmetric stretch (has some net diapole) hence making it IR active. So for your answer symmetric CO2 is IR inactive while asymmetric CO2 is IR active.

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In alcohols O-H stretching and C-O stretching are more important and characteristic to identify the functional group. C-H stretching is more important in compounds like alkanes and aldehydes.

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