C. The lowest mass will be the element in period 1, group 1 (this element is hydrogen)
Hello!
The reaction between HBr and KOH is the following:
HBr+KOH
→H₂O + KBr
To calculate the amount of HBr left after addition of KOH, you'll use the following equations:
![HBr_f=HBr_i-KOH=([HBr]*vHBr)-([KOH]*vKOH) \\ \\ HBr_f=(0,25M*0,64L)-(0,5M*0,32L)=0 mol HBr](https://tex.z-dn.net/?f=HBr_f%3DHBr_i-KOH%3D%28%5BHBr%5D%2AvHBr%29-%28%5BKOH%5D%2AvKOH%29%20%5C%5C%20%20%5C%5C%20HBr_f%3D%280%2C25M%2A0%2C64L%29-%280%2C5M%2A0%2C32L%29%3D0%20mol%20HBr)
That means that after the addition of 32 mL of KOH, there is no HBr left in the solution and the pH should be
neutral, close to 7.
Have a nice day!