A share of $\text{Rs. }10$ was issued at a premium of $\text{Rs. }3$. $\text{Rs. }3$ was payable on application and $\text{Rs. }5$ was payable on allotment (including premium). A shareholder who had applied for $100$ shares was allotted only $50$ shares and due to non-payment of allotment money, his shares were forfeited. In this case, the amount to be debited to Securities Premium A/c on forfeiture of these shares is:

Let's calculate step by step:Application money received:
$$\text{Applied shares}\times \text{Application money per share}=100\times \text{Rs. }3=\text{Rs. }300$$
Application money required for allotted shares:
$$\text{Allotted shares}\times \text{Application money per share}=50\times \text{Rs. }3=\text{Rs. }100$$
Excess application money to adjust on allotment:
$$\text{Excess money}=300-150=\text{Rs. }150$$
Total amount due on allotment:
$$\text{Allotted shares}\times \text{Allotment money per share}=50\times \text{Rs. }5=\text{Rs. }250$$
Breakdown of allotment due:Capital component: $50\times \text{Rs. }2=\text{Rs. }100$ Premium component: $50\times \text{Rs. }3=\text{Rs. }150$ Adjustment of excess application money:According to standard practice, excess application money is applied first towards share capital requirements on allotment, and then towards securities premium.Total Share Capital due on allotment = $\text{Rs. }100$ Remaining excess application money after capital adjustment = $150-100=\text{Rs. }50$ This remaining $\text{Rs. }50$ is applied towards the Securities Premium component.Unpaid Securities Premium:
$$\text{Total Premium Due}-\text{Premium Adjusted}=150-50=\text{Rs. }100$$
At the time of forfeiture, Securities Premium Account is debited only with the amount of premium that has not been realized. Hence, the amount to be debited is $\text{Rs. }100$.