Answer
The missing element is: $^{17}_{8}O$
And the complete reaction is:
$^4_2He + ^{14}_{7}N -- \gt ^{17}_{8}O + ^1_1H$
Work Step by Step
1. Find the mass number of the missing element.
The total mass number of the left side must be equal to that of the right side.
$4 + 14 = ? + 1$
$18 = ? + 1$
$18 - 1 = ? $
$? = 17$
2. Find the atomic number of the missing element.
The total atomic number of the left side must be equal to that of the right side.
$2 + 7 = ? + 1$
$9 = ? + 1$
$9 - 1 = ?$
$? = 8$
3. Identify the symbol of the element with atomic number equal to 8:
It is "O" (Oxygen).
4. Now, write the complete symbol, and substitute it on the reaction.
$^{17}_{8}O$
$^4_2He + ^{14}_{7}N -- \gt ^{17}_{8}O + ^1_1H$
