3. The number of significant figures in an answer to a stoichiometry problem is determined only by
OA
OB
the number of significant figures in the mole ratio used to
solve the problem.
the number of decimal places in the molar masses of
substances in the chemical equation.
the number of significant figures of any measured quantities in
the problem.
the number of significant figures in the molar masses of
substances in the chemical equation.
Oc
OD

i would say b

explanation:

but i think i would need more information than that

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