The question is incomplete. Here I copy the complete question with the missing information:
What are likely formulas for the following molecules. Supply the missing digit.
Choose 1 if the element appears in the formula a a single atom.
Hydrogens are bonded to the preceeding atom in the formula:
(a) CH?OH: ____
(b) CH?Cl₂: ___
(c) CH₃NH?
This is, you must choose the subscript number that replaces the question mark (?) in each chemical formula.
Answer:
(a) CH?OH: 3
(b) CH?Cl₂: 2
(c) CH₃NH?: 3
Step-by-step explanation:
(a) CH? OH:
The carbon atom may have up to 4 bonds. In alcohols one OH radical subsittute one H atom.
So, in methane, CH₄, by replacing on H by one OH group, it is obtained the alcohol CH₃OH.
So, the corresponding subscript for the H atom is 3.
(b) CH? Cl₂:
Starting, again, with methane molecule, CH₄, some H atoms may be replaced by halogen atoms to form halide compounds.
So, when you replace two H atoms with two Cl atoms you obtain the compound CH₂Cl₂, whose name is methylene chloride or dichloromethane.
Then, the corresponding subscript for the H atom is 2.
(c) CH₃NH? : 3
Amines is the general name of the organic compounds where one hydrogen atom is substituted by the amino group NH₃.
So, when one H atom in CH₄ is substituted by NH₃, the compound obtained is CH₃NH₃, whose name is methylamine.
Thus, the missing subscript for the H atom is 3.