Is it always possible to identify something as an element compound pure substance or mixture just by looking at it

In which layer of earth do most earthauakes occur a_ inner core b_outer core c_mantle d_crust

It takes 945.kj/mol to break a nitrogen-nitrogen triple bond. calculate the maximum wavelength of light for which a nitrogen-nitrogen triple bond could be broken by absorbing a single photon.

If a polyatomic ionic compound has gained two hydrogen ions, then how does its name begin?