#01
Wordplay
What has keys, but no locks; space, but no room; and you can enter, but never leave?
A Keyboard
#02
Hard
The more of this there is, the less you see. What is it?
Darkness
#03
Math
If you multiply me by any other number, the answer remains the same. What am I?
Zero (0)
#04
Logic
What has hands, but can’t clap?
A Clock