Is magnesium hydroxide a strong alkali

No, magnesium hydroxide is a medium strong alkali.
The pH of a chemical substance is relative, which is determined by the ionization degree of its aqueous solution. The more active the metal, the greater the degree of ionization in water.
The stronger the pH is, the stronger the magnesium hydroxide is. Because of its ionization degree in water, the magnesium hydroxide can only belong to a medium strong alkali (the solubility of magnesium hydroxide is very small, the solution is very weak, and sometimes it is treated as a weak alkali). Heating to 623K (350 ℃) means dehydration and decomposition: Mg (OH) 2 → MgO+H2O, which is easily soluble in acid or ammonium salt solutions.
Extended data:
For magnesium salt manufacturing, sugar refining, pharmaceutical industry, daily chemical industry, etc. At the same time, the water vapor it emits can also be used as a smoke suppressant. Magnesium hydroxide is an excellent flame retardant with triple functions of flame retardancy, smoke suppression and filling in the rubber and plastic industry.
Store in a cool and ventilated warehouse, and the temperature should not exceed 37 ° C. It shall be stored separately from oxidants and edible chemicals and shall not be mixed. Keep container sealed. Keep away from kindling and heat source.
The warehouse must be equipped with lightning protection equipment, and the exhaust system should be equipped with grounding devices to conduct static electricity. Explosion proof lighting and ventilation shall be adopted. It is prohibited to use equipment and tools that are easy to generate sparks. The storage area should be equipped with emergency treatment equipment for leakage and appropriate materials.