Not enough data
We couldn't find much for "how does atomic radius increase or decrease horizontally or vertically across the periodic table".
Google doesn't have enough autocomplete data on this phrase — probably means people aren't searching for it in this exact form yet. Try a product, place, or topic people actually look up.
This isn't an error — autocomplete reflects what real people type. If a query is brand new, very niche, or gibberish, search engines don't suggest it. That's honest data, not a bug.