<prompt> Suckback porosity is due to:Attached impurities on undersurface of castingHot spotNo rapid coolingInadequate melting temperature  <response>: Suck-back porosity often occurs at an occlusoaxial line angle or incisoaxial line angle that is not well rounded. A hot spot may retain a localized pool of molten metal after other areas of the casting have solidified. This, in turn, creates a shrinkage void or suck-back porosity. This type of porosity defect can be eliminated by flaring the point of sprue attachment and reducing the mold-melt temperature differentialthat is, lowering the casting temperature by about 30C.Reference: PHILLIPS SCIENCE OF DENTAL MATERIALS, 12th ed page no 227 