What trend in size of the atom do you see as you move down a group?

Which alkaline earth metal has the smallest atomic radius? 

In moving from top to bottom in the same column on the periodic table, what trend is expected for atomic size? 

A portion of a two-dimensional 'slab' of NaCl(s) is shown here (see Figure 8.2) in which the ions are numbered. (a) Which colored balls must represent sodium ions?

With the exception of helium, the noble gases condense to form solids when they are cooled sufficiently. At temperatures below 83 K, argon forms a close-packed solid whose structure is shown below. (c) Based on this comparison would you say that the atoms are held together by chemical bonds in solid argon?