Chemistry

X should have a charge with 2+ as it can chemically combine with CO3^2- to form XCO3.
Therefore, the chemical equation becomes:
XCO3 + 2HCl ---> XCl2 + H2O + CO2
No. of moles of HCl
= 0.25 * 40/1000
= 0.01 mol
No. of moles of XCO3
= 0.01 / 2
= 5*10^-3 mol
Let x be the relative atomic mass of X.
since no. of moles = mass / molar mass,
we have 5*10^-3 = 0.985 / (x + 12 + 16*3)
On solving, x = 137
Hence the relative atomic mass of X is 137.
Note that the relative atomic mass has no unit.