Question

What is the density of krypton gas at STP?

Answer 1

The density of krypton at STP is `"3.74 kg/m"^3"`, or `"0.00374 g/cm"^3"` at STP of `0^"o""C"` `("273.15 K")` and `"1 atm"`.
http://www.engineeringtoolbox.com/gas-density-d_158.html
The calculated density is `"0.0037386 g/cm"^3"`.

Explanation:

How to Calculate Density of Krypton from Molar Mass and Molar Volume.

Molar mass `("MM")` is the atomic weight of an element on the periodic table in g/mol.

`"MM"_"Kr"="83.798 g/mol"`
http://www.nist.gov/pml/data/periodic.cfm

Molar Volume `(V_"m")` at STP is `"22.414 L/mol"`
https://en.wikipedia.org/wiki/Molar_volume

`"Density"=("MM")/(V_"m")`

`"Density"_"Kr"=(83.798 "g"/cancel"mol")/(22.414"L"/cancel"mol")="3.7386 g/L"`

`(3.7386"g")/(1"L")xx(1"L")/(1000"mL")="0.0037386 g/mL"="0.0037386 g/cm"^3"` `("1mL=1cm"^3")`