Acids and alkalis can be classified into strong and weak ones, depending on their extent of ionization or dissociation in water.

Acids

  Strong acids ionizes completely in water.

hydrochloric acid, nitric acid and sulphuric acid are strong acids

  Weak acids ionizes very slightly in water. That is, only a very small percentage of the acid molecules have changed into ions.

ethanoic acid, sulphurous acid, carbonic acid phosphoric acid are weak acids

  Strong acids have lower pH and higher electrical conductivity.

Alkalis

  Same to acids, strong alkalis dissociate completely into mobile ions in water. (And these ions allow them to become great electrolytes.) Contrary, a weak alkali is an alkali which ionizes only very slightly in water.

sodium hydroxide is a strong alkali, and ammonia is a weak alkali

  Strong alkalis have higher pH and higher electrical conductivity.

set-up for comparing the electrical conductivities

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Concentration of Acids and Alkalis