A molecule like H-X is 50% ionic if electronegativity difference of H and X is x eV. The value of 10x is ___________________.

Hint: The difference between the electronegativity of two atoms determines their type of bond. If the difference in electronegativity is more than 1.7, there will be an ionic character to the bond. ... Finally, if the difference in electronegativity is less than 0.4 the bond will have a covalent nonpolar character. The concept of electronegativity was introduced by Linus Pauling in 1932; on the Pauling scale, it is measured using the Pauling scale.

Complete answer:
Electronegativity is a measure of an atom's tendency to attract electrons to a bonding pair. The higher the electronegativity value, the stronger that element attracts the electrons it shares. The most commonly used scale is the Pauling. A value of 4.0 is assigned to fluorine (the most electronegative element), and value ranges down to the less electronegative caesium and francium at 0.7.
Pauling considered the partial ionic character of a bond to be an approximate function of the electronegativity difference between the two bonded atoms. He estimated that a difference of 1.7 corresponds to an ionic character of 50 percent, so a greater difference corresponds to a bond that is predominantly ionic.
A molecule like H-X is 50% ionic if the electronegativity difference of H and X is 1.7 eV.
But as given in question it is equal to x eV.
x eV = 1.7 eV
hence, x = 1.7
therefore, 10x eV = 10 $\times $ 1.7 eV = 17eV
Hence, the value of 10x is 17.

Note:
Always remember, there is no electronegativity difference between two atoms that leads to a pure nonpolar covalent bond.
A small electronegativity difference leads to a polar covalent bond whereas a large electronegativity difference leads to an ionic bond.
Always remember or learn as a fact, A molecule like H-X is 50% ionic if the electronegativity difference of H and X is 1.7 eV.