Electrolysis uses electrical current to break water molecules in to oxygen gas and hydrogen gas. how do you know that this is a chemical change? a. their is a phase change from liquid to gas b. it is a single replacement action c. electric current always causes a chemical change d. chemical bonds in the water molecule are broken

Chemical bonds in the water are broken.
Water is made of hydrogen and oxygen. If an electric current is applied it breaks the compound down into its individual elements that is a chemical change.

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.

there are two significant figures.