The stoichiometric reaction of 516g of dimethyldichlorosilane with...

The dimethyldichlorosilane is ${\left({CH}_{3}\right)}_{2}{SiCl}_{2}$. The molecular mass is $129u$.

Number of moles of dimethyldichlorosilane initially taken $= \dfrac{516}{129} = 4moles$

Applying POAC on Si atom

Moles of tetrameric cyclic product formed $= \dfrac{4}{4} \times \dfrac{75}{100} = 0 . 75moles$

Molar mass of product formed $= 296g / moles$

The mass of product formed $= 296 \times 0 . 75 = 222g$