Answer: Option (D) is the correct answer.
Explanation:
The chemical reaction equation will be as follows.

This means a new substance has been formed and a chemical change has taken place.
A chemical reaction in which heat energy is absorbed by the reactant molecules is known as an endothermic reaction.
For example,
On the other hand, a chemical reaction in which heat energy is released by the reactant molecules is known as an exothermic reaction.
For example,
is an exothermic reaction.
Thus, we can conclude that in the given situation the beaker most likely felt warm because a chemical reaction was producing a new substance.
Answer:
C
Explanation:
A fuel cell uses both hydrogen and oxygen as fuels. At the cathode oxygen is reduced to water according to the equation
O2+4H^+ +4e ------>2H2O
And hydrogen is oxidized at the anode:
2H2------>4H^+ +4e
Fuel cells produce only water as a by product hence they are environment friendly
U-238
The number besides the U means its total molar mass. The molar mass of this element is 238
Molar mass= protons + neutrons
This means that 238= 146 + protons
Do 238 - 146
Answer is 92