Since Loss of mass in 4 days = 5 kg

$\therefore$ Loss of mass in 1 day = $\large\frac{5}{4}$kg

$\therefore$ Pressure due to 15kg = 10 bar

Pressure due to $\large\frac{5}{4}kg = \large\frac{10\times5}{15\times4}$

$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;=0.833 bar$

Hence answer is (b)