How many atoms of oxygen are in 3.45g of Na2SO4

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

The diagram below shows the different phase transitions that occur in matter. which arrow represents the transition in which dew is formed?

Pegmatites are igneous rocks in which the individual minerals are very large. typically, the minerals are all light-colored quartz, feldspar and muscovite. if you were given a black and white photograph of a pegmatite in a quarry (where the rock has been blasted and broken), what physical properties could you use to identify those three minerals in this hypothetical photo? describe each mineral and the specific diagnostic properties. be specific.