Mixture of which one of the following pairs of gases is the cause of occurrence of most of the explosions in mines?

Most mine explosions are caused by ignition of methane mixed with air. Methane (firedamp) is the principal combustible gas liberated from coal seams and forms explosive mixtures with air in the range of roughly 5–15% by volume; the most violent explosions occur near about 10% methane in air, and such methane–air mixtures have been the cause of many coal‑mine disasters [1]. Mining safety guidance therefore focuses on ventilation to keep methane below explosive concentrations and monitoring to prevent ignition by sparks or flames, since methane/air is far more commonly responsible for underground explosions than gases like acetylene or pure hydrogen in typical mining atmospheres [2].

Sources

1. [1] https://laborcommission.utah.gov/wp-content/uploads/2019/11/Fire-Boss.pdf
2. [2] https://www.cdc.gov/niosh/docs/mining/works/coversheet1640.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fniosh%2Fmining%2Fworks%2Fcoversheet1640.html