The last option is always the max of how many you have, up to the max you can open at once, which is 200 for gold/glory/gem/event and 50 for VIP/guild (and a whopping 10 for Chaos Shard). The middle is always the next max, which is 50 for most all of them again, except if you have less than that max, then it becomes 10, and the new max in option 3 becomes whatever you have.
So if you have more than or 200 keys, it’s 1/50/200. If you have 50 or less keys, it’s 1/10/50. If you have between 51 and 199 keys, it’s 1/50/Your Keys.