When uranium is bombarded with neutrons, it undergoes fission. The fission reaction can be written as:
\[U_{92}^{235} + n_0^1 \to Ba_{56}^{141} + Kr_{36}^{92} + 3x + Q(energy)\]
Where three particles named $x$ are produced and energy Q is released. What is the name of $x$?
A) Electrons
B) Alpha particles
C) Neutrons
D) Neutrino

Hint: We know that any type of nuclear reaction also follows the laws of conservation of mass. Thus, we can say that the mass of reactants in the nuclear reaction is equal to the mass of the products. Using the law of conservation of mass we can obtain the mass of the unknown entity and thus detect the type of sub-atomic particle in the nuclear reaction.

Complete step by step answer:
The nuclear reaction is given as:
\[U_{92}^{235} + n_0^1 \to Ba_{56}^{141} + Kr_{36}^{92} + 3x + Q(energy)\]
We have to first calculate the sum of the atomic numbers or the number of protons in the Left Hand Side of the nuclear reaction:
Total number of Protons in LHS is equal to $92 + 0 = 92$

Similarly, we will also obtain the sum of atomic numbers or the number of protons in the Right Hand side of the nuclear reaction as well:
Total number of protons in RHS is equal to $56 + 36 = 92$

Thus, we can conclude that the unknown subatomic particle has no protons or no positive or negative charge. Thus the answer cannot be (B) alpha particles or (A) electrons.
Now, we have to obtain the sum of atomic masses of the Left Hand side of the nuclear reaction:
Total atomic mass of the reactants or LHS is equal to$235 + 1 = 236$
Similarly we can also obtain the sum of atomic masses on the Left hand side of the nuclear reaction:

Total atomic mass of the products or RHS is equal to $141 + 92 + 3x = 233 + 3x$
Since, we know that nuclear reactions also follow the Law of conservation of mass. We can say that the total atomic mass of the reactants or LHS is equal to the total atomic masses of the products or RHS. Thus:
$\
236 = 233 + 3x \\
\Rightarrow x = 1 \\
\ $
Thus, we find that the subatomic particle has no positive or negative charge but it has unit mass.
Since, we know that neutrinos have no atomic mass. Thus, x is not a neutrino.
Only, neutrons have unit mass and no net electric charge. Hence the unknown subatomic particle $x$ is a neutron.

Hence, (C) is the correct answer to this problem.

Note: A nuclear reaction also follows the law of conservation of mass and thus, we can use the law of conservation of mass to find the unknown quantity of mass in other numerical problems as well.