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.
Note that there is a 3d subshell, but it is not filled until period 4, such giving the period table its characteristic shape of two rows at a time. All of the period 3 elements occur in nature and have at least one stable isotope.