If a vector A is multiplied by a real number (say n), the vector of same nature is obtained but its magnitude is n times that of A.

Yes, if the angle between the two vectors is more than 90^o but less than 270⁰. (cosΘ is negative)

II)Cr2+ is reducing agent as its configuration changes from d4 to d3, when it is oxidized to Cr3+ .The d3 configuration have a half-filled t2g level which is very stable. On the other hand, the reduction of Mn3+ to Mn2+ results in the half-filled (d5) configuration which has extra stability hence Mn3+ acts as oxidizing agent.

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