Answer:
Measure 74.2 g Na2CO3 and add H20 until the final homogeneous solution has a volume of 7.00 L
Explanation:
The best procedure is
Mole of

= 0.700 mol
The mass of

= 74.2 g
So as per the above calculation, the option 3 is correct as the solution volume is 7.00 L so the same is to be considered
hence, all other options are wrong
I really don’t know but I think you should be more specific
The atomic number of Hydrogen is 1, and the mass is 1.008.