Step-by-step explanation:
The reaction equation for this reaction is as follows.
![NaOH + HCl \rightarrow NaCl + H_(2)O](https://img.qammunity.org/2021/formulas/chemistry/high-school/86zvrxroqqiviw04bslgw3p4x4chpyhzph.png)
The given data is as follows.
= ?,
= 20 ml
= 0.859 M,
= 10.1 ml
Hence, we will calculate the original concentration of HCl as follows.
![M_(1)V_(1) = M_(2)V_(2)](https://img.qammunity.org/2021/formulas/chemistry/high-school/n1w3ylxed7xchmydcx3dkemvbqajict3kx.png)
![M_(1) * 20 ml = 0.859 M * 10.1 ml](https://img.qammunity.org/2021/formulas/chemistry/high-school/pckmp5glo6fxapbyl27e9wv36bp4sfarcx.png)
= 0.434 M
Thus, we can conclude that the original concentration of the HCl is 0.434 M.