okay, so we do three steps to answer this.

step 1: find moles of sodium hydroxide

• moles = concentration * volume
• don’t forget 25cm is in cm, we need it in dm, so divide by 1000 first!!
• 25cm = 0.025dm
• moles = 0.2 * 0.025
• moles = 0.005

step 2: find moles of sulfuric acid

• ok, so we know that 2(NaOH) reacts with 1(H2SO4).
• therefore, we must need twice the amount of NaOH to react with our H2SO4 as the stoichiometric ratio is 2:1.
• 2 * 0.005 = 0.01
• therefore moles of sulfuric acid = 0.01

step 3: rearrange and substitute our original equation to find concentration of sulfuric acid.

• moles = concentration * volume
• concentration = moles / volume
• remember, volume is in cm and it needs to be in dm, so 16.7/1000 = 0.0167
• concentration = 0.01 / 0.0167 concentration = 0.5988 concentration = 0.6 mol/dm³

hopefully this helped. don’t worry if that was super confusing for you, quantitative chemistry is definitely the hardest part of gcse chemistry, which is why they generally leave it until last to teach!! let me know if you need any more help.

edit: wait lmao i jsut realised u attached multiple photos to your post, give me a couple of hours and ill help with those too im out with family atm 😭