$A$ coil of wire of radius $r$ has $600$ turns and a self-inductance of $108 \ mH$. The self-inductance of a coil with the same radius and $500$ turns is: (in $mH$)

Which of the following is not correctly matched?

How many moles of $KMnO_4$ are required to oxidize $1 \ mol$ of $FeC_2O_4$ in an acidic medium?

$A$ ray of light of intensity $I$ is incident on a parallel glass slab at point $A$ as shown in the diagram. It undergoes partial reflection and refraction. At each reflection, $25\%$ of incident energy is reflected. The rays $AB$ and $A'B'$ undergo interference. The ratio of $I_{max}$ and $I_{min}$ is (in $: 1$)

Assertion $(A)$: White tin is an example of a tetragonal system.
Reasoning $(R)$: For a tetragonal system,$a=b=c$ and $\alpha=\beta=\gamma \neq 90^{\circ}$. The correct answer is

The total number of $\sigma$ and $\pi$-bonds in pyrophosphoric acid are respectively