I need help on question 2, 3 and 4

L QUESTIONS 1 Define the term standard solution. 2 Explain why phenolphthalein (pH>7) is used as an indicator in the titration in part 2 of the experiment? 3 Oxalic acid is a diprotic weak acid. What do you mean by this statement. 4 What is your observation/colour change at the end point of the titration in part 2 of the experiment? 5 In a titration exactly 40 cm3 of a strong diprotic acid (H2X) of unknown concentration is neutralised by a sodium hydroxide solution (NaOH) of concentration 0,1 mol.dm-3. The reaction is represented by the balanced equation given below. H2X(aq) + 2NaOH(aq) - NazX(aq) + 2H20({) A burette shown below is used to measure the initial and final volume of sodium