A metalloid is an elements that has some characteristics of metal and other of non-metals. In a periodic table, it is somewhere in between the metals and non-metals.
Looking to a periodic table, we have Na to the far left, so it must has metal characteristics.
Ar is to the far right, it is a noble gas, so not metalloid.
Zn is quite close to the right side, however it is in the groups of transition metals, so it is still a metal and must have metal characteristics.
As is even more to the right, exactly where the metal characteristics of elements start to change to non-metals, so As is probably the one with metalloid characteristics.