Which type of chemical reaction does this equation exemplify? synthesis decomposition double replacement single replacement

The answer is: single replacement.

Single replacement is reaction where neutral element metal or nonmetal become an ion as it replaces another ion in a compound.  

In this balanced chemical reaction magnesium (Mg) replaces copper (Cu).

Magnesium changes oxidation number from 0 to +2 (oxidation) and copper changes oxidation number from +2 to 0 (reduction).

Reactivity series is an empirical progression of a series of metals, arranged by their reactivity from highest to lowest (alkaline metals have highest reactivity and Noble metals lowest reactivity):  

K > Ba > Sr > Na > Ca > Mg > Be > Al > Mn > Zn > Cr> Fe > Cd > Co > Ni > Sn > Pb > H(in acids) > Cu > Hg > Ag.

Metal higher in the reactivity series will displace another and it will be oxidized.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.