What is the definition of a Lewis base? a substance that donates a proton
a substance that donates electrons to form a covalent bond
a substance that accepts electrons to form a covalent bond
a substance that when dissolved in water increases hydrogen ion concentration

The definition of a Lewis base is: C. a substance that accepts electrons to form a covalent bond.

What is a Lewis base?

A Lewis base can be defined as a specie of an ionic or chemical compound that contains an empty orbital which allows it to donate an electron pair (two or more electrons) to form a covalent bond.

This ultimately implies that, a Lewis base is a chemical substance that accepts an electron pair (two or more electrons) to form a covalent bond.

In Chemistry, some examples of a Lewis base include the following:

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the definition is : a compound or ionic species which can donate an electron pair to an acceptor compound.

so as far as i know i know the answer is: a substance that accepts electrons to form a covalent bond.

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Explanation:

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.