Which two ions have the same electron configuration?

a) na+ and o2- b) li+ and f- c) ca2+ and br- d) na+ and o3-

A) Na+ and O2-

Explanation:

To know the electronic configuration, one has to determine the numbers of electrons present in each atom.

Na+ means a sodium atom that has lost one valence electron. A Sodium atom  initially has 11 electrons, but having lost an electron making it 10 electrons remaining with electron configuration of 1s2 2s2 2p6.

O2- means oxygen atom that has gained two valence electrons. An oxygen atom  initially has 8 electrons, having gained two electrons makes it 10 electrons with electron configuration of 1s2 2s2 2p6. same as Na+

The purpose of gaining or losing electrons is to attain a stable duplet or octet structure.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.