How many unpaired electrons does a neutral As atom have?

Arsenic has 3 unpaired p electrons when neutral

Explanation:

Arsenic's electron configfuration is [Ar] 3d¹⁰ 4s² 4p³. The [Ar] can be ignored because we know all noble gasses have fully paired electrons. The full 3d and 4s orbitals can be knocked out as well because full shells/orbitals of any kind are always fully paired. That leaves the 4p orbital with 3 electons. You might think that two would pair up and you'd have one unpaired left over, but according to Hund's rule, "All orbitals will be singly occupied before any is doubly occupied." Therefore, since p orbitals offer three orbital spaces, each of the three 4p electrons occupies each space singly and unpaired.

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explanation:

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.