Final answer:
Estradiol is the form of estrogen that is available in topical skin cream formulations, used commonly for hormone replacement therapy.
Step-by-step explanation:
Among the options provided, estradiol is the estrogen that comes in topical skin cream form. Estradiol is a form of the hormone estrogen which is commonly used in hormone replacement therapy for menopausal symptoms and can also be applied topically to the skin.
Estriol, another form of estrogen, is also available in topical formulations, but it's less commonly used than estradiol. Conjugated estrogens and ethinyl estradiol are typically administered in other forms, such as oral or transdermal but not typically as creams. Ethinyl estradiol is more known for its use in oral contraceptive pills.