Which of the following substances is an alpha1 agonist used as a nasal decongestant?

Phenylephrine is the correct answer as it is an alpha1 adrenergic agonist commonly used as a nasal decongestant. When administered, phenylephrine stimulates alpha1 receptors on the smooth muscle of blood vessels in the nasal passages, causing vasoconstriction. This vasoconstrictive effect reduces edema and congestion in the nasal mucosa, thereby helping to relieve symptoms associated with nasal congestion.

In regards to the other options, ephedrine is a mixed-acting sympathomimetic that can act on both alpha and beta adrenergic receptors and is not classified solely as an alpha1 agonist. Pseudoephedrine, while also used as a nasal decongestant, primarily acts on the release of norepinephrine and has some effects on both alpha and beta receptors, rather than being a selective alpha1 agonist. Albuterol is a selective beta2 agonist primarily used in the treatment of asthma and chronic obstructive pulmonary disease, and it does not have the desired properties to function as a nasal decongestant.