There are many ways to descale a kettle

(Some more successful than others)

The limescale in your kettle is mostly chalk, calcium carbonate (CaCO3), which is a base.

To remove a base you ideally need an acid. Agreed, you could use a stronger base to remove the limescale. Bicarbonate of soda, aka sodium bicarbonate, sodium hydrogen carbonate (NaHCO3) is commonly claimed as being useful for descaling a kettle, but then again you could scrub your garden path with a toothbrush. Its not ideal, its going to take a while - there are more efficient ways.

You could also use a base/acid combination such as baking powder. Baking powder is a usually a mix of sodium bicarbonate (a base) and cream of tartar (tartaric acid). The two when added to water fizz away producing carbon dioxide. When added to limescale the baking powder will fizz away with the limescale as well, but removing the limescale will be a slow old job as its busy doing something else.

So, its best to use an acid, and there are several available.

Hydrochloric acid, this stuff is just dangerous, its not suitable for a domestic enviroment. Avoid!

Phosphoric acid, is a powerful descaler, but its not a nice chemical to work with:

Phosphoric Acid is a corrosive chemical and contact can irritate and burn the eyes.

It can irritate the nose, throat and lungs causing coughing and wheezing.

Phosphoric acid also has some rather complicated handling and storage requirements. All in all its best avoided.

Vinegar, which contains acetic acid. Its safe and is a common item in most kitchens, but vinegar has a few drawbacks:

Its a faily weak acid. 1 teaspoon of vinigar is mostly water, so it is going to take a while to work.

Vinegar is known for its strong flavour, which is going to be difficult to get rid of. Lots and lots of rinsing.

Vinegar flavour tea, hmmmm yum! 🤣

Lemons, which do actually contain citric acid. They're safe and also another common kitchen item, but lemons also have a few drawbacks:

Like vinegar, lemon juice is mostly water, so it too will be slow - about an hour to descale the average kettle.

And again, lemon juice has a strong flavour and odour which will take some getting rid of.

Lemon scented coffee, it might catch on! 🙄

However, when purified and concentrated Citric Acid has some useful properties.