When a metal `X` is treated with cold water, it gives a basic salt `Y` With molecular formula `XOH` (molecular mass `= 40`) and liberates a gas `Z` which easily catches fire. Identify `X , Y` and `Z` respectively 

Options

A. `Na`, `H_2`, `NaOH`
B. `Na`, `NaOH`, `H_2`
C. `H_2`, `Na`, `NaOH`
D. None of the above

Answer

B

Explanation

Molecular formula of `Y = XOH`
Let atomic weight of metal `X` is `a`.
Then, molecular mass of `XOH = a + 16 + 1 = 40` (Given)
`a = 40 - 17 = 23`
Thus, metal `X` is sodium `(Na)` because `23` is the atomic weight of sodium metal. Sodium reacts with as
`2Na+underset("Cold")(2H_(2)O)toundersetY(2NaOH)+undersetZ(H_(2))uparrow`
Sodium `(Na)` gives hydrogen gas `(Z)` on reaction with cold water.
So, `Y` is `NaOH` (sodium hydroxide)
`Z` is `H_(2)` (hydrogen gas).