My brain says, "What is the negative logarithm of the hydrogen ion concentration known as?"
Wait, wait. Let me guess.
pH? Yeah, that.
But I never trusted teachers. I had 4 used college chemistry books, and 3 physics texts. (We didn't have the web back then.)
As for critical thinking, it's not different from scientific method. Take a hypothesis and its antithesis, take 'em out for a drive.
ALWAYS be trying to prove yourself wrong.
After repeated failures to be wrong, you might find yourself on the right track.
Don't put ego on the line. That's a whole different subject. In hard sciences ego is bad, unless you're a fundraiser.