The key equation is
Q=mc Delta T,
where Q is the heat energy required to heat a mass, m,
though a change in temperature of Delta T and c is the heat capacity of the material (found in books!). Typical units are Q in Joules or J, m in kg and Delta T is in either Kelvin, K, or degrees Celsius ""^oC. The units of c depend on the other units used but J // kg ""^o C is typical.
we look up c for water (textbook, the internet, etc)
c=4181 J// kg ""^o C
m=250 g=0.250 kg
Delta T= T_"final" -T_"initial"=100 ""^oC-0 ""^oC=100 ""^oC
Q=(0.250 kg)(4181 J // kg ""^o C) (100 ""^o C)
Q=(0.250 cancel{kg})(4181 J // cancel{kg} cancel{""^o C}) (100 cancel{""^oC})
Q= 104525 J