Which of the following statements is correct for any thermodynamic system?

$100^{\circ} C$ temperature wala ek garam tambe ka tukda $30^{\circ} C$ temperature wale talab mein dala jata hai. Tamba thanda hokar $30^{\circ} C$ par aa jata hai,jabki talab bahut bada hone ke karan apne prarambhik taapman par bana rehta hai. Tab,

$A$ measure of the degree of disorder of a system is known as

Why can't the efficiency of a heat engine ever be $100 \%$?

During phase change,entropy

The graphs below show the entropy versus energy $U$ of two systems $1$ and $2$ at constant volume. The initial energies of the systems are indicated by $U_{1, i}$ and $U_{2, i}$,respectively. The graphs are drawn to the same scale. The systems are then brought into thermal contact with each other. Assume that,at all times,the combined energy of the two systems remains constant. Choose the most appropriate option indicating the energies of the two systems and the total entropy after they achieve equilibrium.