When setting up a conversion, where does the initial unit go in the conversion factor?

All these conversion factors are equal to 1. If it doesn't seem obvious at first, think about it for a second. Realize that 1 minute is equivalent to 60 seconds. Simply replace 1 minute in the fraction with its equivalent 60 seconds and it becomes clear that 60 seconds / 60 seconds = 1. Numerator and denominator are equivalent; they are just expressed differently.

Explanation:

1 a

2 d

3 a

4 c

explanation:

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).