The answer to the riddle "What can you break but not touch?" is "your word" or "a promise." This riddle is considered to be of medium difficulty.
According to The Organic Mind, solving riddles is very good for the human brain. It is a form of brain training that engages the prefrontal cortex and, when practiced regularly, can improve brain speed, memory, attention, flexibility and problem solving.
Riddles and brain teasers are especially great for children. In addition to improving problem solving and critical thinking skills, riddles help kids to improve their vocabulary and reading comprehension skills and introduce them to intellectual humor.
Other medium-difficulty riddles are:
In a tunnel of darkness lies a beast of iron. It can only attack when pulled back. What is it? The answer is "a bullet."
In a drawer, there are 26 white socks and 34 black socks. If a person is blindfolded, how many socks must he draw before he can be sure to have a matching pair? The answer is "three."
How many animals did Moses take on the ark? The answer is "zero." Noah took animals on an ark.
What asks no questions but demands an answer? The answer is "a telephone" or "doorbell."