The cell membrane is a flexible structure that surrounds both plant and animal cells. The arrangement of molecules within the cell membrane makes it semi-permeable. That is, the cell membrane allows some substances to easily diffuse into and out of the cell, but it prevents the diffusion of other substances. Plant and animal cell diagram The cell wall is a rigid structure that surrounds plant cells. The materials found in the cell wall protect the plant cells and give plants structural support

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metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.