Which of the following is incorrect regarding osteoporosis?

Which of the following disorders is a genetic disorder?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$:
Osteoporosis is characterised by decreased bone mass and increased chances of fractures.
Reason $(R)$:
Common cause of osteoporosis is increased levels of estrogen.
In the light of the above statements,choose the most appropriate answer from the options given below:

Low level of $Ca^{2+}$ ions in muscles results in

Which of the following muscular disorders is inherited?

Which sentence is true for the disease Tetany?