2KNO3 —-> 2KNO2 + O2 if 25g of KNO3 is heated, find: (1) What is the mass of KNO2 formed? (2) What is the volume of O2 formed at RTP?

The mass of KNO₂ is 21 g; the volume of O₂ is 3.0 L.
Part (1) is a problem.
You must make the following conversions:
mass of KNO₃ → moles of KNO₃ → moles of KNO₂ → mass of KNO₂
The balanced equation is
2KNO₃ → 2KNO₂ + O₂
The molar mass of KNO₃ is (39.098 + 14.007 + 3× 15.999) g = 101.102 g
25 g KNO₃ × ##(1″mol KNO₃”)/(101.102″g KNO₃”)## = 0.2473 mol KNO₃
(2 + 2 guard digits).
The molar mass of KNO₂ is (39.098 + 14.007 + 2 × 15.999) g = 85.103 g
0.2473 mol KNO₃ × ##(2″mol KNO₂”)/(2″mol KNO₃”)× (85.103″g KNO₂”)/(1″mol KNO₂”)## = 21 g KNO₂
(2 significant figures)
Part (2) is a problem.
You must convert
moles of KNO₃ → moles of O₂ → volume of O₂
0.2473 mol KNO₃ × ##(1″mol O₂”)/(2″mol KNO₃”)## = 0.1236 mol O₂
Room temperature and pressure are not well defined. I will assume that RTP = 1 atm and 25 °C.
We can use the to calculate the volume of O₂.
##PV = nRT##
##T## = (25 + 273.15) K = 298.15 K
##V = (nRT)/P = (0.1236″mol” × 0.08206″L·atm·K⁻¹mol⁻¹” × 298.15 “K”)/(1″atm”)## = 3.0 L
Hope this helps.