Which compound can undergo an addition reaction? 1?

Only 2. Addition reactions require double bonds to be broken and are a characteristic of compounds with double bonds like alkenes. The rest of the options have no double bonds as you can see the carbons have the formula of alkalies. The only alkene is 2 the other compounds can be seen to be alkanes because they fit the general formula of alkanes. Each carbon is saturated and has four single bonds.

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plasma - state of matter made up of electrically charged particles