State the First Law of thermodynamics. Name the physical quantity that remains conserved in this law ?

Explanation

**Step-by-Step Solution:**

1. **Understanding the First Law of Thermodynamics**: The First Law of Thermodynamics is a fundamental principle that relates to the conservation of energy within a physical system. It states that the total energy of an isolated system is constant. Energy can neither be created nor destroyed; it can only be transformed from one form to another.

2. **Statement of the First Law**: The First Law can be mathematically expressed as:
\[ Q = W + \Delta U \]
...