$BCG$ vaccine is used against:

What is the quarantine regulation associated with?

Based on the compounds of group $15$ elements, the correct statement($s$) is (are)

$(A)$ $Bi _2 O _5$ is more basic than $N _2 O _5$

$(B)$ $NF _3$ is more covalent than $BiF _3$

$(C)$ $PH _3$ boils at lower temperature than $NH _3$

$(D)$ The $N - N$ single bond is stronger than the $P - P$ single bond

Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

If the curves $\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$ and $\frac{x^2}{25}+\frac{y^2}{16}=1$ cut each other orthogonally,then $a^2-b^2$ equals to