Question

which of the following elements is considered a metalloid: he mg rn si which of the following elements is considered a rare - earth element: u w ca ne which element is known as a representative element *

Explanation:

1. Metalloids have properties intermediate between metals and non - metals. Silicon (Si) is a well - known metalloid. Helium (He) is a noble gas, magnesium (Mg) is a metal, and radon (Rn) is a noble gas.
2. Rare - earth elements are a set of 17 chemical elements in the periodic table. None of the options U (uranium), W (tungsten), Ca (calcium), Ne (neon) are rare - earth elements. There seems to be an error in the options provided for the rare - earth element question as none of these are rare - earth elements.
3. Representative elements are elements from groups 1, 2 and 13 - 18 in the periodic table. Without seeing the options for the third question, we can't answer it. But for the first two:

Answer:

1. Si
2. None of the above (as U, W, Ca, Ne are not rare - earth elements)