Find the total number of $6^{\mathrm{th}}$ period elements from the given atomic numbers?

81,63,80.50,54,48,86

The atomic number of Thallium, Europium, mercury, and Radon are 81,63,80 and 86 respectively. All the given element is from the sixth period.

The rare earths, or lanthanides, are present throughout six period. Europium is one of many lanthanides that are well-known for having magnetic characteristics. Although many other period 6 metals, including Europium, mercury, and Radon are extremely toxic.

Hence, the total number of $6^{\mathrm{th}}$ period elements from the given atomic numbers is 6.