The `"OLIVINE"` series of minerals consists of crystal in which `Fe^(2+)` and `Mg^(2+)` ions may substitute for each other causing susbstitutional impurity defects without changing the volume of unit cell. In `"OLIVINE"` series of minerals, `O^(2-)` ions exist as fcc with `Si^(4+)` occupying one-fourth of `OVs` and divalent metal ions occupying one-fourth of `OVs` and divalent metal ions occupying one-fourth of `TVs`. The density of "forsterite" (magnesium silicate) is `3.21 g cm^(-3)` land that of "fayalite" (ferrous silicate) is `4.34 g cm^(-3)`. If in "forsterite mineral" bivalent `Mg^(2+)` ions are to be replaced by unipositive `Na^(o+)` ions, and if `Na^(o+)` ions are occupying half of `TV_(s)` in`fcc` lattice, the arrangement of rest of the constituents is kept same, then the formula of the new solid is:A. `Na_(2)SiO_(4)`B. `Na_(2)SiO_(3)`C. `Na_(4)SiO_(4)`D. `Na_(2)Si_(2)O_(6)`