Which of the following elements has the greatest atomic radius?
al
s
si
c

Considering the definition of atomic radius,  aluminum Al has the greatest atomic radius.

The atomic radius represents the distance between the nucleus and the valence shell (the outermost). By means of the atomic radius it is possible to determine the size of the atom.

However, you cannot isolate a single atom and measure its radius. Consequently, the atomic radius is determined indirectly, considering its immediate environment and its interaction with the surrounding atoms. So the atomic radius can be defined as half the distance between the nuclei of two adjacent atoms.

When moving from left to right any period in the table, the number of internal electrons of each of the elements in that period remains constant, while the charge on the nucleus increases. The electrons located in the outermost orbitals then feel a greater “effective nuclear charge”, being attracted with greater force towards the nucleus, which causes the atomic radius to decrease.

Going down the periodic table, along the same group, the effective nuclear charge remains relatively constant while the number of occupied levels increases. Consequently, the atomic radius increases.

In summary, the atomic radius increases from right to left in one period and down in a group.

So, the order of the atomic radius from highest to lowest is  Al, Si, S and C.

Finally, aluminum Al has the greatest atomic radius.

Learn more:

The answer to your question is: Al, Si have the greatest and S, C have the smallest.

Explanation:

Atomic radius increases from right to left in the periodic table.

Atomic radius increases from the upper section to the lower section of the periodic table.

Order of the atomic radius from highest to lowest.

Al, Si, S and C

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.

it's filtration, but this is an assumption so my apologies if i got this