Answer
(a) $4$
(b) $5$
(c) $8$
(d) $15$
Work Step by Step
When we count the number of atoms in a formula unit, an element with no subscript means there is one atom of that element in that compound, and subscripts tell us how many atoms of a particular element are in a compound. When a group of elements are enclosed in parentheses and followed by a subscript, that means the subscript pertains to all of the elements inside the parentheses.
(a) There is one lanthanum atom and three fluorine atoms in this compound for a total of $4$ atoms in one formula unit.
(b) There are two indium atoms and three sulfur atoms in this compound for a total of $5$ atoms in one formula unit.
(c) There are two sodium atoms, one hydrogen atom, one phosphorus atom, and four oxygen atoms in this compound for a total of $8$ atoms in one formula unit.
(d) There is one calcium atom, four hydrogen atoms, two phosphorus atoms, and eight oxygen atoms in this compound for a total of $15$ atoms in one formula unit.
