Fluorosis disease is caused due to the reaction of ...... with excess of fluoride in the body.

Which oxide of nitrogen is obtained when ammonium nitrate is heated at $250\,^oC$?

$2, 3$-dimethylhexane contains tertiary,secondary,and primary carbon atoms,respectively:

An object is projected with a velocity of $20 \ m/s$ making an angle of $45^\circ$ with the horizontal. The equation for the trajectory is $h = Ax - Bx^2$,where $h$ is height,$x$ is horizontal distance,and $A$ and $B$ are constants. The ratio $A : B$ is $(g = 10 \ m/s^2)$.

The circle $4x^2 + 4y^2 - 12x - 12y + 9 = 0$

Let $A = \{x_1, x_2, x_3, x_4\}$ and $B = \{y_1, y_2, y_3, y_4\}$. $A$ function $f: A \to B$ is defined. The number of one-one functions such that $f(x_i) \neq y_i$ for $i = 1, 2, 3, 4$ is equal to: