The doctor knows that people taking the medicine may sleep better just because they expect the medicine to work. how can he be sure of whether the medicine really works?

The best test would be doing a double-blind test between the person who is receiving the medicine so that they don't know if they received a placebo or not and the person giving the medicine does not know if the participant is receiving a placebo or not.

However, a placebo test can simply be done. This is where the patient received a medicine that does not have any medicinal effects and see if the person sleeps better. If they say they did, they have fallen under the placebo effect.

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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.