[bobbert]

Although I got this question right, why would the last 2 options not work? I thought that shifting left always meant decreasing K and shifting right always mean increasing K. This may have something to do with the hint "Some changes may affect the equilibrium position, but not the value of the equilibrium constant." When is this hint applicable?

[Borek]

When is this hint applicable?

In general - always, assuming the temperature doesn't change.

[bobbert]

ok but why wouldnt adding SO2 or removing SO3 also increase K?

[Borek]

It won't change K, which is - as the name implies - constant.

It will change Q - reaction quotient, which looks exactly like K - for a moment, but then the system won't be at equilibrium. It will start reacting and Q will start to change till Q=K.

Q is something that describes current state of the system, K is a value Q will reach when the system gets to equilibrium. K is constant, Q can take any value.