We can taste and tell which one of the solution is acidic and which one is basic.

For sugar solution and salt solution: Taste will be sweet and salty. and we can hence conclude their taste is not sour or bitter. So, they come in category of neutral substances.

For Tamarind solution the taste will be sour, hence we can conclude it is acidic in nature.

For Baking soda solution, the taste will be bitter, hence we can conclude it is basic in nature.