Question: have you taken the organic and general chem series yet?
If you've not finished one of these, I would advise against taking the MCAT before completing them. These questions are very basic and should be covered in the first few weeks of both the General and Organic Chemistry lectures.
With that said, I will try to help:
Energy is released when bonds are formed (lower energy state, generally "good" for everyone involved), and energy is consumed when they are broken (higher energy state, generally unfavorable to all parties). However, molecules are constantly shopping around for the lowest energy state possible, and often times the breaking of bonds will allow them to form new bonds and reach a lower energy state. Think of a free energy reaction diagram.
To break a "triple bond," one must supply enough energy to break 1 sigma and 2 pi bonds. However, there is much less energy associated with the breaking/forming of pi bonds than there is with sigma bonds. So triple bonds are often said to be highly stable (not always the case, obviously) because one has to supply enough energy to break 3 bonds.
To reiterate, sigma bonds have larger bond dissociation energies (BDE) than pi bonds. But a triple bond contains 1 sigma and 2 pi bonds, while a single bond contains only 1 sigma bond. Pi electrons are more reactive because a molecule can redistribute electrons to form sigma bonds and get to a lower energy state. Think: halogenation of alkenes and alkynes.
Bond strength: triple > double > single
BDE: sigma bond > first pi bond > second pi bond
Also keep in mind, when someone says "pi electrons are more reactive," that they are not talking about breaking the entire triple bond. Often, the pi electrons of the double or triple bond will simply form additional sigma bonds with new atoms and the original sigma bond will be left intact.
I hope that helps some - I'm extremely scatterbrained atm and I wish I had the time to consult my general chemistry book for the proper terms, but I hope this is at least intelligible.
