Heat energy = MCΔT; where m is the mass, c is the specific heat capacity; while ΔT is the change in temperature.
Mass is 100 g , while change in temperature 50°C and heat energy is 23.5 kJ or 23500 j
Hence; 23500 = 100 × c ×50
c = 23500/5000
= 4.7 j/g/°c or 4700 J/Kg/°C
The substance is ammonia since it has the specific heat capacity is 4.7 J/g/°C