Given elements /symbol with A# Given element charge/ion 1)h-1. -1, +1
2)Na-11. 1
3)Br-35. 2
4)Mg-12. 3
5)AI-12. 4
6)F-9. 5
7)O-8. 6
8)CI-17. 7
9)K-19. 8
10)Ca-20. 9
11)N-7. 10
12)C-6. 11

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Explanation:fight

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