See i dont think there should be any problem in not showing capital asset in the return of income. But an issue here will be the tax authority will ask for the source of investment and if the source can be substantiated then there might be no issue apart from penalty u/s 271 (I) (c) . But here as there is no tax sought to be evaded and only the purchase of property is not disclosed then there should be no issue. As far as the selling is concerned i would suggest u show that in return of income and capital gains can be avoided by investing in modes specified u/ s 54, 54ec, 54f.