Electrons, everything is pretty much based around the likeliness of electrons to be swapped or shared between atoms
It's 1 because there is only one electron on the outer shell.
So to balance an equation, you need to get the same amount of each type of element on either side of the --> . So you pretty much are given the subscripts in the equations and you need to add coefficients (just normal numbers) in front of any formula that needs it, keeping anything balance.

turns into

These coefficient numbers are the molar ratios, so 2 moles of KCl3 for every 3 moles of O2 so 1. 3:2
Then you can use these ratios of find out how many moles of one thing are needed if you are given the amount of another.

and use cross multiplication to solve for whatever you don't know
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Answer:
elecreonegativity is the attraction of a bonded atom for the pair of electrons in a covalent bond. this can occur if:
- the nuclear charges are different
- the atoms are different sizes
- the shared pair of electrons are closer to one nucleus than the other