Which seismic wave refracts and cannot penetrate the core

P waves and S waves travel through the interior of the earth. P waves are the Primary waves and S waves are the Secondary waves.

    P waves can travel in both solid as well as in liquid (outer core) whereas S wave can travel only through solid. When P waves enters the outer core, it gets deviated and again enters the outer core with further deviation.

               In case of S waves, once it reaches the core-mantle boundary, it reflects to the side of it, forming a shadow zone commonly known as the S wave shadow zone (103°-103°). Thus it cannot penetrate through the outer core.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

these nuts