Answer:
A) ⁴He₂
Explanation:
²³⁸U₉₂ → ²³⁴Th₉₀ + A
To obtain the missing element (A), we have to first find it's atomic and mass numbers.
The mass number is the sum total of the protons and neutrons in an atom. It is usually equal to the superscript in an atom. for example in ²³⁸U₉₂ the mass number is 238.
The atomic number is the total of the protons in an atom. It is usually equal to the subscript in an atom. for example in ²³⁸U₉₂ the atomic number is 92.
In a chemical eqation, there's conservation of mass.
With this, mass number of products = mass number of reactants. same thing for the atomic number.
Mass number of Product = 238
Mass number of Reactant = 234 + x
238 = 234 + x
x = 238 - 234 = 4
Atomic number of product = 92
Atomic number of reactant = 90 + y
92 = 90 + y
y = 92 -90 = 2
So the atomic number of the missing element is 2 and its mass number is 4. ⁴A₂.
Among the elements, the only match is ⁴He₂. So the correct option is A
