Chain Rxn is an addictive flash game that can be found on Facebook. Here's are some strategies and tips for getting a high score:
Don't waste time on the early levels. You won't start making big points until level 5 or so.
You score more from a staggered chain explosion than from one where multiple balls hit the same source. In the following example four balls are exploded each time. But the first method results in 10,000 points [100 + 800 + 2700 + 6400], the second only scores 2,500 points [100 + 800 + 800 + 800]. You can extrapolate this out and see how this will make a huge difference, particularly in the later levels.
Keeping trick #2 in mind, it is always good to start in a corner. You have a better chance of getting a stringed chain explosion when starting from the corner, as the balls can initially hit it from only one direction.
Track the balls for a while, and plan the initial explosion for when you can see several balls coming in a steady stream from the same direction (like shown in the first "good" example).
There are no penalties for failed attempts. Take your time and be patient. By starting in the corner it will take more attempts before you finally clear a level. But when you do clear it, your score will on average be much higher.
By utilizing these tips you can easily score 40 million or more. Have fun!