The catalytic activity of transition metals and their compounds is ascribed mainly to (1) their chemical reactivity (2) their magnetic behaviour (3) their unfilled d-orbitals (4) their ability to adopt variable oxidation states

The catalytic activity of transition metals and their compounds is ascribed mainly to
(1) their chemical reactivity (2) their magnetic behaviour
(3) their unfilled d-orbitals (4) their ability to adopt variable oxidation states
by

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(4) their ability to adopt variable oxidation states
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