Final answer:
Alcohol has the lowest ignition temperature among the substances listed, making it easier to catch fire. Liquids with low boiling points tend to have low flash points and autoignition temperatures.
Explanation:
Alcohol has the least ignition temperature among the substances listed. Ignition temperature refers to the minimum temperature at which a substance catches fire and burns without the need for an external ignition source. In this case, alcohol, being a liquid with a relatively low ignition temperature, can easily catch fire compared to petrol, phosphorus, and diesel.
As combustion is a reaction in the vapor phase, liquids with low boiling points tend to have low flash points and autoignition temperatures due to their significant vapor pressures. Alcohol, being a liquid substance, falls into this category and has a low ignition temperature.
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