What type of energy sublevel is being filled by the elements in Groups III A / 13 through VIII A /18?

How many photons of light are emitted when an electron in a hydrogen atom drops from level 4 to level 1?

Valence electrons are:

Element X has two natural isotopes:  X-63 (62.930 amu) and X-65 (64.928 amu).  Calculate the atomic mass of the element X given the abundance of X-63 is 69.09%.

Which one of the following is the best representation of the titration curve that will be obtained in the titration of a weak acid (0.10 mol L–1) with a strong base of the same concentration?  

Which one of the following is the best representation of the titration curve that will be obtained in the titration of a weak acid (0.10 mol L–1) with a strong base of the same concentration?  

Trihydroxybenzoic acid (THB) is a not-so-weak acid with an ionization constant:  Ka = 2.1 × 10-2.  Calculate the and the pH of a 0.050 molar solution of THB

In preparing for succession, the senior generation has certain responsibilities. One of these is that the

A 0.200 M solution of an acid, HA, has a pH = 3.50.  What is the value of the ionization constant Ka for this acid?

Select the pair of substances in that an acid is listed followed by its conjugate base.