(i) The law $a^m \times b^n$ can be combined into a single power only when the bases are the same or the exponents are the same. The correct law is $a^m \times b^m = (ab)^m$.
Taking an example with $a = 2, b = 3, m = 2$ and $n = 3$,
$$\begin{aligned}\Rightarrow a^m \times b^n = 2^2 \times 3^3 = 4 \times 27 = 108\\[1em] \Rightarrow (ab)^{mn} = (2 \times 3)^{2 \times 3} = 6^6 = 46656\end{aligned}$$
Since, L.H.S. ≠ R.H.S.
Hence, the given statement is False.
(ii) We know that 100 = 102
Solving R.H.S.,
$$\begin{aligned}\Rightarrow (100)^{-10}\\[1em] \Rightarrow (10^2)^{-10}\\[1em] \Rightarrow 10^{-20}\end{aligned}$$
Since (10)-100 ≠ 10-20,
Hence, the given statement is False.
(iii) As the reciprocal of $a^{-m} = a^m$
Solving,
$$\begin{aligned}\Rightarrow \Big(\frac{3}{7}\Big)^{-2}\\[1em] \Rightarrow \Big(\frac{7}{3}\Big)^{2}\end{aligned}$$
The reciprocal of $\Big(\frac{7}{3}\Big)^{2}$ is $\Big(\frac{3}{7}\Big)^{2}$ and not $\Big(\frac{7}{3}\Big)^{2}$.
Hence, the given statement is False.
(iv) Solving L.H.S.,
$$\begin{aligned}\Rightarrow (-a)^{-m}\\[1em] \Rightarrow \frac{1}{(-a)^m}\end{aligned}$$
When $m$ is odd, $(-a)^m = -a^m$ and so $(-a)^{-m} = -\frac{1}{a^m}$, which is not equal to $\frac{1}{a^m}$.
For example, taking $a = 2$ and $m = 3$,
$$\begin{aligned}\Rightarrow (-2)^{-3} = \frac{1}{(-2)^3} = \frac{1}{-8} = -\frac{1}{8}\\[1em] \Rightarrow \frac{1}{2^3} = \frac{1}{8}\end{aligned}$$
Since, L.H.S. ≠ R.H.S.
Hence, the given statement is False.
(v) We know that,
$a^m \times a^n = a^{m+n}$
$$\begin{aligned}\Rightarrow 10^5 \times 10^5\\[1em] \Rightarrow 10^{5+5}\\[1em] \Rightarrow 10^{10}\end{aligned}$$
Since, L.H.S. = R.H.S.
Hence, the given statement is True.
(vi) We know that,
$a^m \times a^n = a^{m+n}$ and $a^0 = 1$
$$\begin{aligned}\Rightarrow p^{\frac{-2}{5}} \times p^{\frac{2}{5}}\\[1em] \Rightarrow p^{\frac{-2}{5}+\frac{2}{5}}\\[1em] \Rightarrow p^{0}\\[1em] \Rightarrow 1\end{aligned}$$
Since, L.H.S. = R.H.S.
Hence, the given statement is True.
(vii) We know that,
$a^m \times a^n = a^{m+n}$
$$\begin{aligned}\Rightarrow (-8)^{-3} \times (-8)^{-4}\\[1em] \Rightarrow (-8)^{-3+(-4)}\\[1em] \Rightarrow (-8)^{-7}\end{aligned}$$
Since (-8)-7 ≠ (-8)-12,
Hence, the given statement is False.