To solve Qs 1., use the following formula.
For two vectors A and B,
||A⃗ ×B⃗ ||= |A⃗ | | B⃗ |sin(θ)
In water the solubility can be seen as.
Ksp value is found
Fe(OH)2 is more soluble in water than Fe(OH)3 because its Ksp is 22 orders of magnitude (1022 !) larger.
Please note that Ksp value is the "Solubility Product Constant" and this has been found experimentally, and is available online for reference.