In which equation does the oxidation of the underlined compound occur? with explaination
a 2cu + c → co2 + cu
b fe2o3 + 3c0 - 2fe + 3co2
c 2mg + o2 - 2mgo
d mno2 + 4hc1 - mncl2 + 2h20 + cl2

The element oxidized is the one whose oxidation number INCREASES

Explanation:

And thus

+

I

I

  2CuO

+

C

→

2

0

C

u

+

C

O

2

↑

⏐

⏐

And here while copper (as  

C

u

2

+

) is reduced, carbon is oxidized,  

0

C

→

+

I

V

C

.

The second reaction represents the reduction  

C

r

(

V

I

+

)

to  

C

r

(

I

I

I

+

)

C

r

2

O

2

−

7

+

14

H

+

+

6

e

−

→

2

C

r

3

+

+

7

H

2

O

(

i

i

)

And the oxidation of ethanol to carbon dioxide:

H

3

C

−

C

H

2

O

H

+

H

2

O

→

2

C

O

2

+

8

H

+

+

8

e

−

(

i

i

i

)

i.e.  

H

3

−

I

I

I

C

−

−

I

C

H

2

O

H

→

2

+

I

V

C

O

2

We takes  

4

×

(

i

i

)

+

3

×

(

i

i

i

)

to eliminate the electrons

3

H

3

CC

H

2

O

H

+

3

H

2

O

+

4

C

r

2

O

2

−

7

+

56

H

+

+

24

e

−

→

8

C

r

3

+

+

28

H

2

O

+

6

C

O

2

+

24

H

+

+

24

e

−

To give finally

3

H

3

CC

H

2

O

H

+

4

C

r

2

O

2

−

7

+

32

H

+

→

8

C

r

3

+

+

25

H

2

O

+

6

C

O

2

Dichromate ion

is reduced to  

chromic ion