Which of the following is an element that is a diatomic gas in its standard state? A) Zn, B) Pt, C) Li, D) O, or E, U.
Let’s first identify which elements these symbols represent. Zn is zinc, Pt platinum, Li lithium, O oxygen, and U uranium. The prefix di- in diatomic refers to the number two. So, a diatomic molecule consists of two atoms bonded together. This question refers to a diatomic gas molecule.
Standard state is a hypothetical condition in which a substance exists in a specific form and the air pressure around that substance is one bar. We do not need to consider temperature because it is not part of the standard-state definition. And different thermodynamic tables report the temperature under standard conditions differently.
Note that all elements on the periodic table can potentially exist as solids, liquids, or gases, depending on the conditions, such as temperature or pressure. This periodic table shows us the phase or state which elements exist in in their standard state. We can see that most elements exist as a solid under standard conditions, only two as liquids, mercury and bromine, and several in the gas phase. The noble gases are highly stable and do not react under normal conditions. They exist as monoatomic particles or single atoms.
Now, let’s identify where answers A to E are located on the periodic table. We can see that A, zinc; B, platinum; C, lithium; and E, uranium are all solids in their standard state. They are also all metals. All metals are solid in their standard state, except for mercury. Because zinc, platinum, lithium, and uranium are all solid in their standard state, none of these can be the answer. Option D, oxygen, is a gas in its standard state. And the element exists as a diatomic gas molecule. So, the element which exists as a diatomic gas in its standard state is option D, oxygen.