Which element would you expect to be less metallic?

(a) Cs or Rn (b) Sn or Te (c) Se or Ge

When we move across a period from left to right then there will occur an increase in electronegativity and also there will occur an increase in non-metallic character of the elements.

As cesium (Cs) is a group 1 element and radon (Rn) is a group 18 element. Hence, cesium (Cs) is more metallic in nature than radon.

This means that radon (Rn) is less metallic than cesium (Cs).

Tin (Sn) is a group 14 element and tellurium (Te) is a group 16 element. Hence, Te is less metallic than Sn.

Selenium (Se) is a group 16 element and germanium (Ge) is a group 14 element. Therefore, selenium being more non-metallic in nature is actually less metallic than Ge.