Question

Then tell if this is an exothermic or an endothermic reaction and how you know.

Answer 1

use pic above

Answer 2

horizontal line A represents- nothing yet lol :)
next u see a peak at B
whats happening is that the bond between atoms in a compound broke and now they all are atoms ready to react and form a product
this is endothermic reaction since you need energy to break bonds in compound to form atoms (because it's not that compounds react, it is Atoms that react to for compounds)
so D (which is dashed vertical lines) is representing amount of activation energy (specific amount of energy needed to break the bond)
now after peak you see the line goes down meaning energy value drops to below the value where u started reaction at A
that means your value of energy will be negative and this reaction is releasing heat, that means it is exothermic reaction.
as the atoms make a new compound they release energy that they were given originally and in this case they released more energy than D- activation energy which was given to them that's is why this reaction at C is exothermic

Answer 3

overall the whole reaction is exothermic, reason is
because energy released (by new compound formed) is more then energy given (to starting reactants so that bonds break in compounds to make atoms)