The $pK_a$ of a weak acid is $4.8$. What should be the ratio of $\frac{[\text{acid}]}{[\text{salt}]}$,if a buffer of $pH=5.8$ is required?

Which one of the following is not correct?

Two different radioactive elements with half-lives $T_{1}$ and $T_{2}$ have undecayed atoms $N_{1}$ and $N_{2}$ respectively,present at a given instant. The ratio of their activities at this instant is

The self-inductance of a choke coil is $10 \, mH$. When it is connected to a $10 \, V$ $DC$ source,the power loss is $20 \, W$. When it is connected to a $10 \, V$ $AC$ source,the power loss is $10 \, W$. The frequency of the $AC$ source is ....... $Hz$.

Knowing the properties of $H_{2}O$ and $D_{2}O$,do you think that $D_{2}O$ can be used for drinking purposes?

If the slope of one of the lines given by $ax^2+2hxy+by^2=0$ is two times the other,then: