In an exothermic chemical reaction, the energy that is given off by the reaction comes from a. the surroundings b. an external heat source c. stored energy in the chemical bonds of the reactants

Remark

Exothermic means heat given up by the chemical reaction. So A is incorrect. Heat is taken up by the surroundings. The reaction does not take energy from the surroundings.

B is also incorrect. Think of all those movies involving car explosions. Those happen because someone torches the vehicle. If you add heat to an exothermic reaction, generally you get one big nasty quick explosion. Beautiful colors, lots of danger. The torch only gets things going. After that the chemicals provide all kinds of energy of their own.

C This is the precise way exothermic reactions occur. You need just enough initial energy to get things going, then the break down of bonds gives away the energy they have stored.

12000j is work done

gas and liquid