Using eno (also known as Eno fruit salt or antacid) instead of baking powder in a cake recipe is not recommended. While both eno and baking powder are leavening agents used to make cakes and other baked goods rise, they are not interchangeable.
Baking powder is specifically formulated for baking purposes and contains a combination of an acid (usually cream of tartar) and a base (usually baking soda). When mixed with moisture and exposed to heat, baking powder produces carbon dioxide gas, which creates bubbles in the batter and causes the cake to rise.
Eno, on the other hand, is primarily used as an antacid to relieve heartburn and indigestion. It also contains baking soda, but it is combined with citric acid, which is a different acid than what is typically used in baking powder. Eno is not meant to be a direct substitute for baking powder in baking recipes.
If you don't have baking powder on hand and need a substitute, you can try using baking soda, but keep in mind that you'll need an acidic ingredient (such as buttermilk, yogurt, lemon juice, or vinegar) in the recipe to activate the baking soda properly. The acidic ingredient reacts with the baking soda to produce the necessary carbon dioxide gas for leavening. The substitution ratio is typically 1/4 teaspoon of baking soda for every 1 teaspoon of baking powder.
In general, it's best to stick to the ingredients specified in the recipe for the most reliable and consistent results. If you don't have a particular ingredient, it's a good idea to find a suitable substitute rather than making a random substitution that could negatively affect the outcome of your cake.