How do you know which elements increases or which elements decreases on a Ionisation graph? Like how can you figure out that these elements will increase on the graph and which will decrease?

Explanation:

There is a trend in the periodic table.

I.E increases up the group and across the period. So you know that metals have less I.E compared to non-metals.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.