If X is the symbol of an element, which pair correctly represents isotopes of X

Bose-einstein condensation occurs at what temperature?

What does x represent in the formula for the compound xcl4?

Silver tarnishes as silver metal reacts with hydrogen sulfide, h2s, in the air. in this reaction, dark silver sulfide, au2s, covers the surface of silver. when silver is polished, this coating of silver sulfide can be removed from the surface. this makes the silver shiny again. enter the coefficients that balance the tarnishing reaction equation. (type 1 for no coefficient.)