Assertion: The carbons lost as ${\mathrm{CO}}_2$ in the Krebs cycle come directly from acetyl CoA.
Reason: These carbons are lost always and cannot be put to any use.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Refer to the schematic diagram of Krebs citric acid cycle given below:

How many of the enzymes involved in the pathway are dehydrogenases?
  
1. 2
2. 3
3. 4
4. 5

Refer to the diagram given below:
 

Identify the incorrectly matched pair: