Right answer is SiCl4 , SnCl4...because, there...Sn & Si are tetra valent...they easily from +4 ions by releasing Cl...which fumes in atmosphere to produce white fumes...

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White fumes are commonly observed when certain compounds react with moist air. These fumes are usually formed due to the reaction of the compound with water vapor in the air, resulting in the formation of a new compound that is volatile and appears as a white smoke or fumes.

To determine which pair of compounds gives white fumes when reacted with moist air, let's analyze the given options:

a) AlCl3, NiCl2:
- Aluminum chloride (AlCl3) is a compound that is hygroscopic, meaning it readily absorbs moisture from the air. However, it does not produce white fumes when it reacts with moist air.
- Nickel chloride (NiCl2) is also hygroscopic but does not produce white fumes when exposed to moist air.
- Therefore, this pair of compounds does not give white fumes when reacted with moist air.

b) TiCl4, SiCl4:
- Titanium tetrachloride (TiCl4) is a compound that reacts vigorously with water, producing white fumes of titanium dioxide (TiO2). This reaction is exothermic and releases heat.
- Silicon tetrachloride (SiCl4) is also highly reactive with water, producing white fumes of silica (SiO2).
- Therefore, this pair of compounds (TiCl4, SiCl4) does give white fumes when reacted with moist air.

c) SiCl4, SnCl4:
- As mentioned earlier, silicon tetrachloride (SiCl4) reacts with water to produce white fumes of silica (SiO2).
- Tin tetrachloride (SnCl4) is also hygroscopic but does not produce white fumes when exposed to moist air.
- Therefore, this pair of compounds (SiCl4, SnCl4) does give white fumes when reacted with moist air.

d) All of these:
- The correct answer is d) all of these. Both options b) and c) mentioned above give compounds that produce white fumes when reacted with moist air.

In summary, the pair of compounds that give white fumes when reacted with moist air are TiCl4, SiCl4, and SiCl4, SnCl4.