Which of the following describes a study that is "longitudinal"? A study that follows people for an extended period of time to see if they develop a disease or condition.
A study that looks at people in one location, to reduce any bias introduced by varying locations.
A study that follows people taking a drug or placebo for 6 weeks to see if they develop a disease or condition.
A study that follows people taking medication in different locations, to see if their location impacts the medication's effectiveness.

the right answer is c i just did the question.

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