Which metal will react spontaneously with a Cr3+ ion but not with a Ca2+ ion? A) Co
B) Li
C) Mg
D) Pb
E) Metals will all react in the same way with these ions.

I know the answer is Mg, but why?

the answer is minerals.

where are the choice options?

the transfer of heat by electromagnetic radiation is called thermal radiation . it is usually carried out by electromagnetic waves in an energy range just below the visible spectrum, which is the infrared range.

so the answer would be radiation.

: )