What is the use of the folding rule and give one care and maintenance of it​

i don't do that but Folding rules can be used for measuring both small spaces and longer distances. They can be transported easily once they are folded up, making them useful when working in the field. Folding rules can also be used to measure a point which is difficult to reach.but it's stu.pid lol

Explanation:

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