Find the element: 1. A group 12 metal that was once used in thermometers, but now it’s know to be poisonous.
2. Has 3 valence electrons and 4 energy levels.
4. The only metalloid with 3 valence electrons.
5. It’s most common isotope has 5 neutrons.

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