The newton is the si unit of what physical quantity?

Newton is the SI unit of force.

Newton is the name of a British scientist and the name of unit is to honour him.

The unit is actually Kg.m/s2

The unit can be derived by the formula.

Take the example of weight. It's formula is W = mg . We know that the unit of mass is kg and gravity is m/s2 so the unit of weight becomes kg.m/s2

This unit is known as a Newton.

It is always given a capital letter because it is someone's name. Other units that are always capitalised (upper case) are Ampere (Amp), Watt, Volt, Coulomb, Kelvin, Celsius, Fahrenheit, Curie, Roentgen because they are also people's names.