2C(s) + 2H2(g) > C2H4(g) exothermic or endothermic?

A__ is two or more substances that are together in the same place but are not chemically combined

Me i dont know what to do! the table compares the number of electrons in two unknown neutral atoms. comparison of electrons atom number of electrons a 10 d 11 use this information to determine the number of valence electrons in the atoms. which of the following correctly compares the stability of the two atoms? both are unreactive. both are highly reactive. a is unreactive and d is reactive. a is reactive and d is unreactive.

How many grams of sodium chloride are in 250ml of a 2.5m naci solution