And the service in these stores is also very good. Generally, the price of an eye exam in Wal-mart, Costco and Target optical can range from less than $50 (if you have an eye exam at a retail store or optical chain) to $100 or more (if you have an eye exam at a medical clinic or private eye doctor's office).
What is true about the elements of a period? (Select all that apply.) a.They have the same number of electron shells. b They have similar chemical characteristics. c They have similar physical characteristics.
In the periodic table the elements are arranged into periods and groups. The periodic table is made up of loots of diffrent elements. A row of elements across the table is called a period. Each period has a number: from 1 to 7. Period 1 has only 2 elements in it: hydrogen and helium.