Ms. Fleming's class sets up an experiment involving pendulums. You can see in the picture that a pendulum is a "bob" attached to a string which hangs from a fixed point, allowing the bob to swing back and forth. They hook a 10 gram bob to a 12 inch string, and measure the time it takes for the bob to swing back and forth one time as 2 seconds.
Then the class hooks a 20 gram bob to a 20 inch string and measure the time it takes to swing back and forth as 4 seconds.
Erin hypothesizes that the difference in time is related to the type of string used. What would NOT be a good alternative explanation?

A) That the difference is due to the different masses
B) That the difference is linked to the length of the string
C) That the difference is due to the temperature of the bobs

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.