Let's write the equation

According to law of conservation of mass .
- Mass of products=Mass of reactants
Let required value be x




Answer:
<h2>
total no. of electron present in Valency shell is called valency electron </h2><h2>___________________</h2>
<h2>valency shell is that in which last electron is present</h2>
Average distance between gas molecules become double,, hope it helpss