3. Which subatomic particles account for most of an atom's mass? 4. Which subatomic particle accounts for most of an atom's volume?

3. Proton is the subatomic particle which accounts for most of an atom's mass.

4. Electrons are the subatomic particle which accounts for most of atoms volume.

that's what i got you can count the number of atoms

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