Elisabeth Haller. 8:20 AM Due Tomorrow
4 points
An experiment is described below.
A student was interested in comparing sunblock lotions, which contain chemicals that protect the skin from sunburn.
The student purchased three different brands of lotion at three different prices and performed an experiment to see
which one best protected the skin. The lotions cost $3, $5, and $7 for an 8-ounce bottle. The sun protection factor
(SPF) was 30 for all three lotions. The student applied equal amounts of each lotion next to each other on one of her
arms. The three areas covered by the lotions were the same size. The student observed the three areas for color
change after two hours of sun exposure
Identify two conditions that were held constant (kept the SAME) in this experiment.
Class comments

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

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.

the answer is option a.