Experimentally it is found that $$12.8 ~\mathrm{eV}$$ energy is required to separate a hydrogen atom into a proton and an electron. So the orbital radius of the electron in a hydrogen atom is $$\frac{9}{x} \times 10^{-10} \mathrm{~m}$$. The value of the $$x$$ is __________.

$$\left(1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J}, \frac{1}{4 \pi \epsilon_{0}}=9 \times 10^{9} \mathrm{Nm}^{2} / \mathrm{C}^{2}\right.$$ and electronic charge $$\left.=1.6 \times 10^{-19} \mathrm{C}\right)$$

Two concentric circular coils with radii $$1 \mathrm{~cm}$$ and $$1000 \mathrm{~cm}$$, and number of turns 10 and 200 respectively are placed coaxially with centers coinciding. The mutual inductance of this arrangement will be ___________ $$\times 10^{-8} \mathrm{H}$$. (Take, $$\pi^{2}=10$$ )

As shown in the figure, two parallel plate capacitors having equal plate area of $$200 \mathrm{~cm}^{2}$$ are joined in such a way that $$a \neq b$$. The equivalent capacitance of the combination is $$x \in_{0} \mathrm{~F}$$. The value of $$x$$ is ____________.

A body is dropped on ground from a height '$$h_{1}$$' and after hitting the ground, it rebounds to a height '$$h_{2}$$'. If the ratio of velocities of the body just before and after hitting ground is 4 , then percentage loss in kinetic energy of the body is $$\frac{x}{4}$$. The value of $$x$$ is ____________.