What is the external temperature of the liquid nitrogen tank?

Liquid nitrogen can't be placed in a high temperature environment. In summer, the temperature is controlled at about 20 degrees, the room is best ventilated, liquid nitrogen is liquid, and the temperature is low.

The liquid nitrogen tank is well insulated. The external temperature of the tank is air temperature.

the correct answer is... "ambient temperature"

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LN2 comes in containers like this
http://ec-i21.geccdn.net/site/images/large/30912264.jpg
which is liquified at room temperature by compression and is stored under high pressure
the external temperature = the temperature of the room it's stored in.. "ambient temperature"

or can be in containers like this
http://ec-i21.geccdn.net/site/images/n-picgroup/MQL_TY509X4.jpg
which is at ambient pressure and low internal temperature
but the outside of that container will be at ambient temperature

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to those who say the tank is well insulated... not the first one I showed.
to those who say it can't be placed in a high temp environment.. baloney see the first image
to those who say "the tank sits outdoors and is boiling and cools itself.... "geez.. and NO..
.. .it's stored under pressure"

They sit outdoors. The liquid nitrogen is boiling - it cools itself. Ample insulation reduces the loss thru boiling as much a feasible. (In other words, which costs more: a little N2(l) or more insulation?)