It is recognized that, in nuclear reactors, oxygen-hydrogen gas bubbles may form and this formation can lead to an explosion hazard. In this study, numerical investigations are conducted into the collapse and explosion of an isolated oxygen-hydrogen bubble immersed in water. The mathematical model of the bubble's radial motion is based on the compressible form of the modified Rayleigh-Plesset equation of the bubble dynamics. The model also takes into account, in differential form, the heat transfer between the gas and the surrounding inert water. Parametric study on the present model is primarily aimed at delineating the effects of exothermicity of the reactive gas mixture and the initial bubble diameter on the bubble's volume and thermal oscillations under various sustained liquid pressure fields. The exothermicity of the bubble's gas content is varied by changing the mole fraction of the mixture of stoichiometric oxygen-hydrogen with the inert gas, argon, as a diluent. The results show that if the incident pressure pulse is not of sufficient strength, the mixture within the bubble does not ignite and the bubble radius remains below the initial equilibrium value throughout the pulsation period. Under the above conditions, due to the low heat capacity of argon compared to that of oxygen and hydrogen, the maximum gas temperature attained by the bubble increases with the increase in argon content or, equivalently, with the decrease in oxygen-hydrogen content. If the incident pressure pulse is strong enough, the bubble is seen to explode and the maximum gas temperature that the bubble attains depends directly upon the initial oxygen-hydrogen content. When the bubble undergoes ignition, with the increase of exothermicity, the maximum bubble radius increases and the period of the volume oscillation becomes longer. Also, with decreasing initial bubble radius, the liquid threshold pressure for bubble explosion increases, while the period of bubble oscillation decreases.