The correct answer is letter B because both Copper and Iron as reactants have an oxidation number of zero and when they have reacted their oxidation numbers would be different from those.
A redox reaction is a reaction that involves a transfer of electrons from one atom to another and the oxidation numbers of the reactants are different from the oxidation numbers from the products.
Yes you could because the obtuse angle is greater than 90 degrees so if the acute angle is inside the obtuse you could get an right angle or an 90 degree angle
