(A) Melting point of carboxylic acids with even number of carbon atoms is higher than the next higher or lower carboxylic acid with odd 
number of carbon atoms. 
(R) Carboxylic acid with even number of carbon atoms fit closely in the crystal lattice as compared to acids with odd number of carbon atoms.

The carboxyl end and terminal methyl group in even number carbon containing acids lie on opposite side of zig zag chain .This provides more close packing in crystal lattice which results in high melting point. This property is known as alternation effect. This is mostly observed in first ten members of the series.