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.
Groups and periods are two ways of categorizing elements on the periodic table. Here is how to tell them apart and how they related to periodic table trends. Answer: Periods are horizontal rows (across) the periodic table, while groups are vertical columns (down) the table. Atomic number increases both as you move down a group or across a period. Elements in a group share a common number of valence electrons.