<u>Answer: </u>The correct answer is Option B.
<u>Explanation:</u>
First law of thermodynamics states that the energy can neither be destroyed not be formed but it can only be transformed from one form to another.
Here, the internal energy of the system is being transformed to the heat energy and the work done by the system. The equation used to represent first law of thermodynamic is:

where,
represents the internal energy of the system.
Q = heat released or absorbed by the system.
w = work done by or on the system.
Hence, the correct answer is Option B.
The mass in a chemical reaction remains (mostly) the same.
(except for radiation/nuclear fission, in which mass gets converted into energy)
The density of the stone is 5 g/cm³.
Mass = 25 g
Volume = 7 mL – 2 mL = 5 mL = 5 cm³
Density = mass/volume = 25 g/5 cm³ = 5 g/cm³
Just count the number C’s and H’s