The S.I unit of temperature is :

The correct option is Kelvin.

To understand why this is the correct answer, let's look at the standard system of units used worldwide. The International System of Units (abbreviated as SI from the French Système International d'Unités) defines seven base units for seven fundamental physical quantities.

Temperature is one of these seven fundamental physical quantities. The SI base unit for thermodynamic temperature is defined specifically as the Kelvin (symbol: $K$).

Let's examine the other options to understand their relationship with temperature:
1. Celsius (${℃}^{}$) and Centigrade: While Celsius (formerly known as centigrade) is widely used for everyday temperature measurements in most parts of the world, it is a derived unit rather than the primary SI base unit. The relation between Celsius and Kelvin is given by the formula:
$T\left(K\right)=t\left({℃}^{}\right)+273.15$
2. Fahrenheit (${℉}^{}$): This is a scale primarily used in the United States and a few other countries. It is part of the United States customary system of units, not the SI system.

Therefore, the officially recognized S.I. unit of temperature is the Kelvin.