Answer:
Choice A: carbon-12, [tex]^{12}_{\phantom{0}6}\text{C}[/tex].
Explanation:
- The number on the top-left corner of each particle is its mass number.
- The number on the lower-left corner of each particle is its atomic number.
Let
- the mass number of X be A, and
- the atomic number (a.k.a. proton number) of X be Z.
Symbol of X: [tex]^{A}_{Z}\text{X}[/tex].
Consider the two conservation laws:
- Sum of mass numbers on the left-hand side = Sum of mass numbers on the right-hand side.
- Sum of atomic numbers on the right-hand side = Sum of atomic numbers on the right-hand side.
Sum of mass numbers:
- Left-hand side: 9 + 4;
- Right-hand side: A + 1.
Equate the two sides:
[tex]9 + 4 = A + 1[/tex]
[tex]A = 12[/tex].
Thus the mass number of X is 12.
Try the steps above to find the atomic number of X. The number [tex]0[/tex] on the lower-left corner of [tex]^{1}_{0}n[/tex] indicates that the atomic number of this neutron is zero.
[tex]Z = 6[/tex].
Thus the atomic number of X is 6.
What element is X? Refer to a modern periodic table. The element with atomic number 6 is carbon. The symbol for carbon is [tex]C[/tex]. The mass number of this isotope is 12. The answer will be [tex]^{12}_{\phantom{0}6}\text{C}[/tex].
