Who was the first person to come up with the idea of the "atom?"

Democritus

Explanation:

Democritus first introduced the idea of the atom almost 2500 years ago. Democritus was an important philosopher however if your talking about how the atom is today look at first rudimentary   pudding model by JJ Thomson first design then its Neils  Bohr whos model we look at today

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