1 mole of any substance has Avagadro number of molecules and it's weight is equal to its molecular weight.
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Answer 1:
Molecular weight of HNO3 = 63.01 g/mol
Therefore, 1mole of HNO3 = 63.03 g
Hence, 15.7 mole of HNO3 = 63.03 X 15.7
= 989.57 g
Thus, mass of 15.7 mole of HNO3 = 989.57 g
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Answer 2:
Molecular weight of H2O2 = 34.01 g/mol
Therefore, 1mole of H2O2 = 34.01g
Hence, 0.00104 mole of H2O2 = 34.01 X 0.00104
= 0.03537 g
Thus, mass of 0.00104 mole of H2O2 is 0.03537 g
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Answer 3:
Molecular weight of SO2 = 64.07 g/mol
Therefore, 1mole of SO2 = 64.07 g
Hence, 72.1 mmole of SO2 = 64.07 X 0.0721
= 4.619 g
Thus, mass of 72.1 mm of SO2 is 4.619 g
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Answer 4:
Molecular weight of XeF2 = 169.29 g/mol
Therefore, 1mole of XeF2 = 169.29 g
Hence, 1.23 mole of XeF2 = 169.29 X 1.23
= 208.23 g
Thus, mass of 1.23 mole of XeF2 is 208.23 g
Answer : The balanced redox reaction will be,

Explanation :
The given chemical equation is,

In the half reaction method, the number of atoms in each half reaction and number of electrons must be balanced.
The half reactions in the acidic medium are :
Reduction :
......(1)
Oxidation :
.......(2)
Now multiply the equation (2) by 4 and then added both equation, we get the balanced redox reaction.
Thus, the balanced redox reaction will be,

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Hope This Helps!
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Answer:
Advantages :they are used for seeing chemical reactions .
they are used for doing chemical experiment .
they are used for making affective medicines .
Disadvantages :they harms to our environment.
they can make side effects in our body by affective medicines made by chemicals.
while doing different unknown experiments they make explosions which can also harm to us.