copper sulphate solution turns the colour of litmus into red but litmus changes into blue with baking soda solution although both are salts. Give reason why?​

Copper sulphate is an acidic salt: It is the product of the reaction between a weak copper base and a strong acid , H2SO4

Litmus has a red colour in acidic solutions:

Conclusion: Acidic copper sulphate solution turns blue litmus to red

Baking soda is a basic salt : It is the reaction product of a weak acid , CO2 and a strong base , NaOH

Litmus has a blue colour in basic solutions:

Conclusion: basic baking soda solution turns red litmus to blue