Assertion: All nitrogen fixing organisms are bacteria.
Reason: Only bacteria can have mutualistic relationship with roots of plants.

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.

Nitrogen fixation means:
1. releasing nitrogen from dead and decaying materials.
2. conversion of nitrite to nitrate.
3. conversion of nitrate to nitrite.
4. conversion of nitrogen gas into ammonia.

Conversion of ammonium to nitrate during nitrogen cycle is called as:
1. Nitrogen assimilation
2. Denitrification
3. Nitrification
4. Nitratification

A microbially facilitated process of dissimilatory nitrate reduction that may ultimately produce molecular nitrogen (${\mathrm{N}}_2$) through a series of intermediate gaseous nitrogen oxide products is called as:

Reaction carried out by ${\mathrm{N}}_2$ fixing microbes include
(i) 2NH₃ + 3O₂ \(\rightarrow\) \(2NO_2^-\) + 2H⁺ + 2H₂O 
(ii) \(2NO_2^-\) + O₂ \(\rightarrow\) 2NO₃
Select the false statement:
1. (i) is carried out by Nitrosomonas or Nitrococcus
2. (ii) is carried out by Nitrobacter
3. Both (i) and (ii) can be called nitrification
4. Bacteria carrying out (i) and (ii) are usually photoautotrophs