Question

how did Mendel explain that it is possible that a Trait is inherited but not expressed in an organism?? ​

Answer 1

His experiments showed that recessive characters do not get lost. In the F1 generations, all the organisms showed dominant character but in F2 generation recessive character is also shown. This is according to Mendel's law of Segregation.
Hence in F1 generation the recessive character is just not expressed but is inherited.

Answer 2

inheritnce is the transmission of genetically controlled characteristics from one generation to the next ....or law of segregation holds good for this