Amolecule of water (h2o) is made from combining two hydrogen atoms and one oxygen atom.
a.
physically
c.
thermally
b.
ionically
d.
chemically

A molecule of water (H2O) is made from D. Chemically combining 2 hydrogen atoms and 1 oxygen atom.

A molecule of water (H2O) is made from _C. THERMALLY_ combining two hydrogen atoms and one oxygen atom.

It takes two(2) molecules of the diatomic hydrogen gas, combined with one(1) molecule of the diatomic oxygen gas to produce two(2) molecules of water. 

The formation of water from it's elements produces, in addition to water, an exothermic reaction giving out a tremendous amount of energy, 572 kJ to be exact.

The formation of water is also an example of what is called a combustion reaction, where a substance is combined with oxygen.

Temperature and pressure