Mass and energy are conserved is demonstrated by

Options

A. First law of thermodynamics
B. Law of conservation of energy
C. Law of conservation of mass
D. Modified form of `I^(st)` law of thermodynamics

Explanation

To solve the question "Mass and energy are conserved is demonstrated by", we can follow these steps:

### Step 1: Understand the Laws of Conservation
The first step is to understand the fundamental laws of conservation in physics and chemistry. The law of conservation of mass states that mass cannot be created or destroyed in a closed system. The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another.

**Hint:** Look into the definitions of the laws of conservation in physics and chemistry.

### Step 2: Identify the Relevant Law
Next, we need to identify which law encompasses both mass and energy conservation. The first law of thermodynamics, also known as the law of energy conservation, states that the total energy of an isolated system is constant. It can be expressed in a modified form that includes the conservation of mass.

**Hint:** Consider how the first law of thermodynamics relates to both mass and energy.

### Step 3: Choose the Correct Option
Based on the understanding that the modified form of the first law of thermodynamics includes both mass and energy conservation, we can conclude that the correct answer to the question is that mass and energy conservation is demonstrated by the modified form of the first law of thermodynamics.

**Hint:** Review the options provided in the question to select the one that mentions the modified first law of thermodynamics.

### Final Answer
The correct option is the fourth one: the modified form of the first law of thermodynamics, which demonstrates the conservation of both mass and energy.

### Summary of Steps:
1. Understand the laws of conservation of mass and energy.
2. Identify the law that includes both mass and energy.
3. Choose the correct option based on the modified first law of thermodynamics.