Which statement best describes the atoms in a gas? they vibrate in place. they stay in a fixed position. they are closely packed. they move freely in all directions.

            Option-D : They move freely in all directions.

                   The physical properties of gases are well explained by Kinetic Molecular Theory. The key postulates of this theory are;

                              1) Composition: Gases are made up of small particles called molecules. The size of these molecules is very small as compared to the distance between molecules, therefore the actual volume of molecules is taken negligible as compared to volume occupied by them.

                             2) Intermolecular Forces: All the gas molecules present in a container behaves independently because they have no force of interactions between them Hence, the attractive forces are taken negligible or too little.  

                              3) Energies: Gas molecules have greater kinetic energy as compared to solids and liquids. Hence, The gas molecules move randomly. They collide with each other and with the walls of the container which causes pressure.

                  Therefore, due to large spaces, no interactions, small sizes and high energies the gas particles move freely and there position is not stationary.

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.