The smallest group of particles in a crystal that retains the shape of the crystal is called the
a. cube
b. unit cell
c. cage
d. crystal lattice

The correct answer is B.unit cell

Explanation:

An unit cell is an arrangement of particles (atoms, ions or molecules) in a crystal structure. The repetition of the unit cell reproduces the complete crystalline structure of the solid. Depending on how are located the particles, there are different unit cells, for exaple: simple cubic, body-centered cubic, face-centered cubic.

is there multiple choice answers?

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.