Yes, Challenger - although program management knew they were violating a launch constraint (temperature), and it was the low temperature that produced the conditions necessary for SRB failure.

As with any aerospace mishap, it's a chain of events, not just one cause.

Yes, challenger. The O-ring failed, creating a gas exhaust that almost instantly destroyed the main propellant tank.

I believe what it destroyed was the strut holding the booster to the tank. When the strut burned through the assembly came apart and aerodynamic forces did the remainder of the destruction.

Yes, 50% of shuttle losses were due to SRB failures (Challenger)

That's exactly how Challenger was lost.