Question

238/92U arrow 4/2he+ 234/90 blank
The element in the missing box is . (Use the symbol from the periodic table, not the whole name.)

Blank 1:

Answer 1

To solve the nuclear reaction given:

\[
^{238}_{92}U \rightarrow ^{4}_{2}He + ^{A}_{Z}X
\]

We need to balance both the atomic numbers (Z) and mass numbers (A) on each side of the equation.

1. The mass number on the left side is 238 (from U).
2. The mass number on the right side is the mass of the helium nucleus (4) plus the mass of the unknown element (A). Therefore:

\[
238 = 4 + A
\]

Solving for A:

\[
A = 238 - 4 = 234
\]

3. Next, we consider the atomic numbers:

- The atomic number of Uranium (U) is 92.
- The atomic number of Helium (He) is 2.

So, for the unknown element:

\[
92 = 2 + Z
\]

Solving for Z:

\[
Z = 92 - 2 = 90
\]

Now we have:

\[
A = 234
\]
\[
Z = 90
\]

The element with atomic number 90 is Thorium (Th).

Thus, the missing element in the blank is:

**Blank 1: Th**