The goal of this exercise is to understand how to multiply fractions in which the numerical quantities have units. Chemical measurements have units. You will need to label quantities with units and to work with units in your mathematical operations for chemistry problems. In fractions, units are multiplied the same way as the numeric values of the numerators and the denominators. That is, the units of the numerators are multiplied to get the units for the numerator of the answer. Likewise, the units of the denominators are multiplied to get the units for the denominator of the answer. For example, if you are characterizing a span of material that has one atom per three units of length, your calculation would look like:

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.