i just learnt this recently but i need to look through my notes again.
I would say the last one because unlike beta and alpha rays they will have no effect on the mass or atomic number because they are just composed of high energy radiation
MnCl2(aq) is an ionic compound which will have the releasing of 2 Cl⁻ ions ions in water for every molecule of MnCl2 that dissolves.
MnCl2(s) --> Mn+(aq) + 2 Cl⁻(aq)
[Cl⁻] = 0.92 mol MnCl2/1L × 2 mol Cl⁻ / 1 mol MnCl2 = 1.8 M
The answer to this question is [Cl⁻] = 1.8 M
There are 4 atoms in sodium hydrate