Final answer:
Among the listed compounds, NH3 (ammonia) is a base. Without the magnitude of the [H3O+] concentration specified, we cannot accurately determine if a solution with [H3O+] = 1.0 is basic; if it's intended to be 1.0 x 10^-7 M, the solution would be neutral.
Step-by-step explanation:
To identify which of the listed compounds is a base, we need to understand that bases are substances that can accept protons (H+) or release hydroxide ions (OH−). Among the given compounds, H2O (water) can act as both an acid and a base, HCl (hydrochloric acid) is a strong acid, NH3 (ammonia) is a base as it can accept a proton to form NH4+, and C2H5OH (ethanol) is not a common acid or base. Therefore, NH3 is the compound that is a base.
To determine if a solution is basic, we consider the concentration of hydronium ions ([H3O+]). A solution with [H3O+] < 1 × 10−7 M is basic. However, since the question states [H3O+] = 1.0, it seems incomplete, as we need the magnitude order of that concentration (for example, 1.0 M or 1.0 × 10−7 M) to evaluate the acidity or basicity. Assuming the intended meaning is [H3O+] = 1.0 × 10−7 M, the solution would be neutral, not basic.