Which chemical element from group 18 of the modern periodic table, whose atomic number is 10, contains a mixture of three stable isotopes commonly used to make signal and gas lasers and as a refrigerant?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Neon i.e.
- An element of the fourth period is one of the chemical elements in the fourth row (or period) of the periodic table of elements.
- There are 18 elements in the fourth period, starting with potassium and ending with krypton. Calcium is a chemical element with symbol Ca and atomic number 20.
- Calcium is a soft brownish yellow alkaline earth metal, the fifth most abundant element by mass in the Earth's crust.