What is the ground-state electron configuration of krypton (Kr) in noble-gas shorthand notation?

• A. [Ne] $3^s$$2^{}$ $3^p$$6^{}$ $4^s$$2^{}$ $3^d$$1^0$ $4^p$$6^{}$
• B. [Ar] $4^s$$3^d$$1^0$$4^p$$6^{}$
• C. [Ar] $4^s$$2^{}$ $3^d$$8^{}$ $4^p$$8^{}$
• D. [Ar] $4^s$$2^{}$ $3^d$$1^0$ $4^p$$6^{}$

Answer: (D)