If the atomic number of an element remains the same but the number of neutrons has been increased, which factor has been changed in that element?

The mass number has changed.

Explanation: The atomic number is also known as the proton number, and if that changes then the name of the element would also change.  

Since there is a change in mass it suggests a change in the number of neutrons, meaning that you are now dealing with an 'isotope' of that element. Isotopes behave a little differently and some can be radioactive. The mass number you see on the periodic table tends to be the most common or stable number for that element.

Plus i know this because i took this in science class.

Hope this helps :).

i wish i could but this one is weird give me abc and i can solve it.

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