What can be determined if only the atomic number of an atom is known?
(1) the total number of neutrons in the atom, only
(2) the total number of protons in the atom, only
(3) the total number of protons and the total number of neutrons in the atom
(4) the total number of protons and the total number of electrons in the atom

i'm assuming that the correct answer is indeed the first one/ "a"..

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