Which gas is evolved when $SiO_2$ reacts with sodium carbonate?

If $\bar{a}$ and $\bar{b}$ are two unit vectors such that $\bar{a}+2 \bar{b}$ and $5 \bar{a}-4 \bar{b}$ are perpendicular to each other,then the angle between $\bar{a}$ and $\bar{b}$ is

The value of $k$ for which the equation $x^2-4xy-y^2+6x+2y+k=0$ represents a pair of straight lines is equal to ........

If $(1, a)$ and $(b, 2)$ are conjugate points with respect to the circle $x^2+y^2=25$,then $4a+2b$ is equal to

How many of the following plants produce a composite fruit that develops from an inflorescence? Walnut,Poppy,Radish,Fig,Pineapple,Apple,Tomato,Mulberry.

In the circuit shown in the adjoining figure,the reading of the ammeter is .............. $A$.