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NEET levelSingle correct optionDifficulty 1 of 3qa004

A cobalt blue glass is often used while viewing the flame test of a potassium salt contaminated with sodium. Its purpose is to

  1. Aincrease the temperature of the flame so that potassium is excited
  2. Bconvert the sodium ions into a non-volatile compound
  3. Cabsorb the intense yellow light of sodium and transmit the violet-red light of potassium
  4. Dabsorb the violet light of potassium and transmit the yellow light of sodium

Answer: C

Sodium emits strong yellow light at 589 nm that masks the weak lilac emission of potassium. Blue cobalt glass absorbs the yellow and lets the violet and red end through, so the potassium flame can be seen. It does not change the chemistry or the flame temperature.
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