Bromocresol green is an acid-base indicator. It is yellow when the pH is below 3.8. It is blue when the pH is above 5.4. It is green between these values. Bromocresol green is then added to the aqueous solution produced when the chloride of element T is mixed with water. The solution changes to yellow. If an excess of the solid oxide of element U is added gradually to this yellow solution, the indicator changes first to green and then to blue. Which row could identify element T and element U?
- Aelement T: silicon; element U: sodium
- Belement T: silicon; element U: phosphorus
- Celement T: magnesium; element U: sodium
- Delement T: magnesium; element U: phosphorus