Helpp you will get a

HC= Hydrocarbon

CH=benzene

Explanation:

HC is Hydrocarbon, how? -- Hydrocarbon, a category of substances consisting only of hydrogen and carbon.

CH is benzene, how? -- benzene is represented by the empirical formula CH, which indicates that a typical sample of the compound contains one atom of carbon (C) to one atom of hydrogen (H).

(Is this what you meant???)

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

the answer is a! (2.9 x 10^-18 j) hope i could someone. : )