Moving left to right across a row of the periodic table, which of the following values increases by exactly one from element to element? a. isotope number b. atomic number c. atomic mass unit d. mass number

Iknow #2 is d. i just need to know why

Which type of substance ionizes partially and gives off hydrogen ions when dissolved in water? a. strong acid b. strong base c. weak acid d. weak base

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?