Clear as bell

If something is as clear as a bell, it is very clear or easy to understand.   

”I wonder why he misunderstood the instructions. It was clear as a bell.”

Clean hands

Someone who has clean hands is free from fault or any wrongdoing.   

“He who accuses someone of an offense must come with clean hands.”

Chow

This is another name for food.  

“How’s the chow at the school canteen?”

Chink in someone's armour

This refers to a weakness that can be taken advantage of.  

“Only people close to him could see the chink in his armour.”

Chill out

To chill out is to relax, to calm down (‘Cool out’ is also used.)   

“After a busy week they went down the beach to chill out.”

Child's play

A child's play is something very easy and simple to do or accomplish.  

 ”He is a gifted. Physics is child’s play to him.”