When a cell is at rest, what ions can pass through easily?

Background:
Visit http://highered.mheducation.com/sites/0073403490/information_center_view0/index.html and choose the Students edition tab at the left side of the page (you don’t need to sign in). Click on Chapter 4(It is from old book, for more information read chapter 8 in current book “Fundamentals of Human Physiology” by Silverthorn, Pearson education, and then on Animation Quizzes. Open the animations links and view the animations: 1) action potential propagation in an unmyelinated axon (the first animation) and 2) voltage gated channels and the action potential (the sixteenth animation). Take the quizzes under each animation.
Then go to http://faculty.washington.edu/chudler/ap.html
Read through the material. Observe the simulated action potential recording.
Procedure:
Insert the Ph.I.L.S. disk or access the online website.
Do Lab Activity: The Compound Action Potential (#12).
Conclusion:
Attach a screen shot (Ctrl & Prt Scr then paste) of the completed graph from your PhILS journal and Write a general narrative report (NOT scientific format) that discusses what can be learned from the exercise. Discuss a little and be sure to incorporate answers to the following questions in your narrative.
1. When a cell is at rest, what ions can pass through easily?
2. The words “spike” and “impulse” are used in place of what?
3. What is “threshold”?
4.Which ions move through the membrane causing depolarization?
5. Which ions move through the membrane causing repolarization?
6. What causes the sodium channels to open?