The molar mass of an element is equal to
(a) the mass of an atom of the element in grams.
(b) the atomic mass of the element in grams.
(c) the number of atoms in a mole of the element.
(d) the number of atoms in a gram of the element.
(e) the number of electrons in an atom in grams.

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