One way of expressing concentration is by percent. It may be on the basis of mass, mole or volume. Percent is expressed as the amount of solute per amount of the solution. For this case, we are given the percent by mass. In order to solve the amount of solute, we multiply the percent with the amount of the solution.
Mass of solute = percent by mass x mass solution
Mass of solute = 0.0350 x 2.50 x10^2 = 8.75 grams of solute
For every 2 Mol NaOH you would get 1 Mol N2H4
Answer : The final temperature of the copper is, 
Solution :
Formula used :

where,
Q = heat gained = 299 cal
m = mass of copper = 52 g
c = specific heat of copper =
= final temperature = ?
= initial temperature = 
Now put all the given values in the above formula, we get the final temperature of copper.


Therefore, the final temperature of the copper is, 