Phosphorus is a nonmetallic element that plays an important role in biological systems as a component of ATP and the sugar phosphate backbone of DNA.  Elemental phosphorus can exist in several different structural forms, known as allotropes, each exhibiting different chemical properties.  The two most common allotropes of phosphorus are P4 (white phosphorus) and (P4)n (red phosphorus).Figure 1  Structural representation of the P4 and (P4)n allotropes of phosphorusP4 is thermodynamically unstable due to its constrained geometric structure and ignites upon exposure to air.  However, the polymeric structure of (P4)n results in greater thermodynamic stability under ambient conditions.  Upon exposure to intense heat at pressures less than 43 atm, (P4)n sublimes and decomposes into P4.In an experiment, a sealed silica tube containing a sample of solid (P4)n at one end was placed under 1 atm of inert gas.  The sample was continuously heated at 450 °C until all the (P4)n had sublimed.  The resulting vapors were transferred by the inert gas to the other cooled end of the tube, where the vapors condensed into liquid P4.  Further cooling solidified the P4 product, and a 5.74 g sample was collected from the tube.  The heating curve shown in Figure 2 was subsequently obtained for the P4 sample.Figure 2  Heating curve of white phosphorus at a pressure of 1 atm (Note: Heat was supplied at a constant rate during the experiment, and the latent heat of fusion ΔHfusion was measured to be 2.51 kJ/mol.) Question 28Which of the following does NOT describe the phase behavior of P4 at 1 atm of pressure?A.At 30 °C, P4 exists as a solid.B.At 45 °C, P4 exists as a mixture of a solid and a liquid.C.At 280 °C, P4 exists as a mixture of a solid, liquid, and gas.D.At 295 °C, P4 exists as a gas.