Which of the following is a bacterium involved in denitrification?

Which of the following soil microorganisms breaks down plant and animal protein into ammonia?

What is the function of $Pseudomonas$ and $Thiobacillus$ in the $N_2$ cycle?

The nature of $Bacillus \ rimosus$ is:

Match the organisms given in Column $I$ to their functions given in Column $II$ and choose the correct option.

Column $I$	Column $II$
$A$. Thiobacillus	$1$. Free-living nitrogen-fixing cyanobacteria
$B$. Nitrosomonas	$2$. Denitrification
$C$. Nostoc	$3$. Free-living aerobic nitrogen-fixing bacteria
$D$. Azotobacter	$4$. $NH_{3}$ to Nitrite

Codes:
$A \quad B \quad C \quad D$

Plants usually absorb Nitrogen in the form of nitrates because Nitrogen is . . . . . . .