The correct way to write the SI unit of force is

The concept of force is discovered by Sir Issac Newton and after him we have named the SI unit of force as Newton. Option (A) states Newtons which is wrong because Newtons represent multiple units which is not right. And option (C) and (B) are starting with small letters and we know that a name never starts with a small alphabet. Hence Option (D) is right because it is starting with a capital latter as well as it represent a single SI unit force.