Step 1 (Write the income as a sum over slabs).
\[
1{,}70{,}000
=\underbrace{50{,}000}_{0\%}
+\underbrace{10{,}000}_{10\%}
+\underbrace{90{,}000}_{20\%}
+\underbrace{20{,}000}_{30\%}.
\]
\medskip
Step 2 (Compute tax contributed by each slab).
\begin{align*}
\text{Tax on first }50{,}000 &: 0\%\Rightarrow ₹ 0,
\text{Tax on next }10{,}000 &: 10\%\Rightarrow 0.10\times 10{,}000=₹ 1{,}000,
\text{Tax on next }90{,}000 &: 20\%\Rightarrow 0.20\times 90{,}000=₹ 18{,}000,
\text{Tax on last }20{,}000 &: 30\%\Rightarrow 0.30\times 20{,}000=₹ 6{,}000.
\end{align*}
\medskip
Step 3 (Add the slab-wise amounts).
\[
\text{Total tax}=₹(0+1{,}000+18{,}000+6{,}000)=\boxed{₹ 25{,}000}.
\]
\medskip
(Why not the other options?)
₹ 34{,}000 and ₹ 51{,}000 come from incorrectly applying a single high rate to the full income; ₹ 17{,}000 ignores the $30\%$ slab.