An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following.
Na (sodium) possesses all the above properties. It is too soft and can be cut with a knife. It is also very reactive and reacts with oxygen or moisture present in air and produce sodium hydroxide which is highly exothermic reaction producing a lot of heat. It also reacts with water vigorously and burns due to the formation of hydrogen gas. That is why sodium is stored in kerosene oil to prevent any reaction.
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