Lack
This kanji is the same as the radical it comes from. Lack becomes Lack!
If you know the radical you know this.
けつ
か
None
To remember けつ, we use the word "ketsup." It's the perfect blend of ketchup and catsup! You're lacking something in your fridge. You look around, trying to find the ketsup (けつ) you lack. You can't find it, because you lack it.
Imagine having to use regular, ordinary ketchup, or just old, boring catsup on your burger. Or even worse, an actual tomato. BLEH!