Cr2O3+ 2Al -----------> 2Cr+ Al2O3
Cr2O3--------2Cr.
( oxidation no. of cr +3 to +1 means hain of electron so it act as oxidizing agent)
similarly,
2Al------> Al2O3
( oxidation no. of Al +1 to +3 means loss of electron so it act as reducing agent)
Yes, a solid has a fixed volume.
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<span>The problem has to do with oxidation states of the matter. The oxidation state of oxygen will always be -2 with the exception of peroxides which will have a state of -1. The overall balanced state of chemical compounds will be 0, so the oxidation state of Mn in MnO2 will be +4. The oxidation state of MnO4- will then be +7 to balance out to the negative one charge. The state change from +4 to +7 is 3, thus three electrons have to be lost in order for this to happen; a loss of a charge of -3 results in an increase of charge of 3. Oxidation is always the process of 'losing' electrons.
</span><span>E] MnO2(s) MnO4-(aq</span>