Match the following sand mold casting defects with their respective causes.

Defect		Cause
P	Blow hole	1	Poor collapsibility
Q	Misrun	2	Mold erosion
R	Hot tearing	3	Poor permeability
S	Wash	4	Insufficient fluidity

The correct option is P-3, Q-4, R-1, S-2.

To understand why this match is correct, let us analyze each sand mold casting defect and its corresponding cause step-by-step:

1. Blow hole (P) matches with Poor permeability (3)
Blow holes are smooth, round holes or cavities formed on the surface or inside the casting. During pouring, moisture in the sand mold vaporizes to form gases. If the sand mold has poor permeability, these gases cannot escape through the sand pores and instead get trapped inside the molten metal as it solidifies, causing blow holes.

2. Misrun (Q) matches with Insufficient fluidity (4)
A misrun occurs when the liquid metal fails to completely fill the mold cavity, leaving an incomplete casting. This defect is caused by insufficient fluidity of the molten metal, which prevents it from flowing into all the thin sections or corners of the mold before it solidifies.

3. Hot tearing (R) matches with Poor collapsibility (1)
Hot tears (or hot cracks) are tears that occur in the casting as it cools and shrinks during solidification. If the mold has poor collapsibility (meaning it does not easily compress or collapse under the contraction forces of the cooling metal), it restricts the natural shrinkage of the casting, inducing tensile stresses that lead to hot tearing.

4. Wash (S) matches with Mold erosion (2)
A wash is a surface defect characterized by an excess projection of metal on the casting surface. It is caused by mold erosion, where the high-velocity flow of incoming molten metal washes away or erodes the loose sand from the mold surface (specifically near the gate or runner), creating cavities that then fill with metal.