The final temperature of the water after dropping the iron ball has been 60.
The heat transferred by the iron ball can be given by:
Heat (Q) = mcT
Q = heat transferred = 8.4 kJ
Q = 8400 J
m = mass = 200 g
c = specific heat = 4.2 J/g.
T = change in tempertaure = Initial temperature - final temperature
T = Final temperature - 50
8400 J = 200 g 4.2 J/g. (Final temperature - 50 )
Final temperature = 60.
The final temperature of the water after dropping the iron ball has been 60.
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Out of the options, glass is the least fluid. The proof of this also lies in the fact that glass is the most difficult to melt out of all of the mentioned substances, and melting point gives us a rough estimate of the strength of intermolecular forces.
Answer : The mass of helium gas in the balloon is, 1.23 grams.
Explanation : Given,
Volume of helium gas = 6.9 L
First we have to calculate moles of helium gas at STP.
As we know that, 1 mole of substance occupy 22.4 L volume of gas.
As, 22.4 L volume of helium gas present in 1 mole of helium
So, 6.9 L volume of helium gas present in 
of helium
Now we have to calculate the mass of helium gas.
Molar mass of He gas = 4 g/mol
Thus, the mass of helium gas in the balloon is, 1.23 grams.
