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.
Answer:
alloys, iodized water, etC
ANSWER
An atom of element is electrically neutral because the number of positive protons are equal to number of negative electrons.