Which important greenhouse gas,other than methane,is produced from agricultural fields?

Which of the following ions is not tetrahedral?

The harmonic mean of $\frac{a}{1 - ab}$ and $\frac{a}{1 + ab}$ is

In a transistor circuit,when the base current is increased by $50 \mu A$ keeping the collector voltage fixed at $2 \ V$,the collector current increases by $1 \ mA$. The current gain of the transistor is

If $\theta$ is the angle between vectors $\vec{a}$ and $\vec{b}$ and $|\vec{a} \times \vec{b}| = |\vec{a} \cdot \vec{b}|$,then $\theta$ is equal to

The eccentricity of the conic $36x^2 + 144y^2 - 36x - 96y - 119 = 0$ is