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.
Part 3. Survey of Period 1: hydrogen H to helium He. Period 1, the shortest period of the periodic table, only consists of two elements, hydrogen and helium. Although the properties of helium match those of the other Noble Gases, hydrogen does not really fit into any group. A brief summary of their properties is given below.