What mass of H2SO4 is contained in 25g of 15% w/w solution? (Relative atomic mass are H=1amu , S=32amu, O=16amu)

What mass of K3PO4 is required to prepare 400mL solution that contains 6 x 10^21 K3PO4 particles per liter of solution?  ( atomic masses are  K=39amu, P=31amu  O=16amu)

Naturally occurring cobalt consists of only one isotope,⁵⁹Co, whose relative atomic mass is 58.9332
amu. A synthetic radioactive isotope of cobalt, ⁶⁰Co,has a relative atomic mass of 59.9338 amu and is
used in radiation therapy for cancer treatment. A 1.5886 g sampleof cobalt has an apparent

131. Naturally occurring magnesium has an atomic mass of 24.312 and consists of three isotopes. The major isotope is 24Mg, natu- ral abundance 78.99%, relative atomic mass 23.98504. The next most abundant isotope is 26Mg, relative atomic mass 25.98259. The third most abundant isotope is 25mg, whose natural abun dance is in the ratio of 0.9083 to that of 26Mg. Find the relative atomic mass of 25Mg.