So if you take 10 items and put them in 2 groups, you have 5 items per group. (10÷2=5) If you take 10 items and put them in 1 group, you have 10 items. (10÷1=10) If you take 0 items and put them in 100 groups, you have 0 items per group. (0÷100=0)

But there is no way to put 10 items in 0 groups, you still have 10 items, so it wouldn't be zero, but they're not grouped at all so it's not a number (like 10), so you get 10÷0 is invalid or null.