What is the number of protons in a neutral atom with 31 electrons and 38 neutrons?

31

I think. Protons and electrons share the same number as well as the atomic number.

31 protons

Explanation:

Protons are positively charged and electrons are negatively charged so if it is a neutrally charged atom (which most are) the protons and electrons will be equal.

how to make a simple air condition

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).