Q.(A) Read the following text carefully : "A country's total National Income (NI) at the end of the year is ₹ 80,000 crore. During the same year, the Gross Domestic Product (GDP) increased by ₹ 10,000 crore. The depreciation on capital goods was ₹ 2,000 crore and National savings at the end of year is ₹ 15,000 crore. Additionally, country invested ₹ 8,000 crore in new capital goods industries." In the light of above text, categorise the items as 'stock' or 'flow' variables with valid arguments.

Let’s start with something you already know: your pocket money.

Suppose your father gives you ₹500 every week. That ₹500 is a flow — it comes in over a period of time. Now suppose you save ₹200 each week for a month. At the end of the month, you have ₹800 in your wallet. That ₹800 is a stock — it is the amount you have at a particular point in time.

This is the whole idea in a nutshell. A stock is measured at a point in time. A flow is measured over a period of time.

The precise meaning

In economics, the distinction is crucial because it prevents confusion between what you have and what you get.

Examples from your NCERT textbook:

Notice: a stock can change only because of flows. If you add water (inflow) and remove water (outflow), the stock changes. This gives us a simple identity:

In national income accounting, this becomes:

Where:

• $K_t$ = capital stock at the end of year $t$ (a stock)
• $K_{t-1}$ = capital stock at the start of year $t$ (a stock)
• $I_t$ = gross investment during year $t$ (a flow)
• $D_t$ = depreciation during year $t$ (a flow)

Why it matters

If you mix up stock and flow, you make serious errors. For example:

• “India’s national income is ₹200 lakh crore” — that’s a flow (per year).
• “India’s national wealth is ₹1,000 lakh crore” — that’s a stock (at a point).

You cannot compare them directly. A country with a high income (flow) might have low wealth (stock) if it spends everything. A rich country (high stock) might have low current income.

Another classic mistake: “Investment is part of capital.” No — investment is a flow that adds to the stock of capital. Capital is the accumulated result of past investments.

A diagram in words

Imagine a bathtub. The water level at 8:00 AM is a stock. The tap is open — water flows in at 5 litres per minute — that’s a flow. The drain is open — water flows out at 2 litres per minute — that’s another flow. The water level at 8:10 AM is a new stock, higher than before because inflow exceeded outflow.

In the economy: …

The GNP Deflator: From Everyday Intuition to Exam-Ready Concept

Imagine you earn ₹50,000 a month. Next year, your salary goes up to ₹55,000 — a 10% raise. Are you actually better off? Not if the price of everything you buy has also risen by 10%. Your nominal income went up, but your real purchasing power stayed the same.

This is exactly the problem the GNP Deflator solves — but for an entire country's output instead of your salary.

What the GNP Deflator Actually Measures

The GNP Deflator is a price index that measures the average change in prices of all final goods and services included in the Gross National Product (GNP). Unlike the Consumer Price Index (CPI) which tracks only a fixed basket of consumer goods, the GNP Deflator covers everything a country's residents produce — including machinery, government services, exports, and capital goods.

The Formula (NCERT Standard)

The NCERT textbook defines the GNP Deflator as:

Where:

• Nominal GNP = GNP measured at current year prices (includes inflation)
• Real GNP = GNP measured at base year prices (removes inflation)
• The multiplication by 100 converts it into an index number

How It Works: A Step-by-Step Example

Suppose India produces only two things in a year: wheat and steel.

Step 1: Calculate Nominal GNP

Use current year prices × current year quantities for everything.

Step 2: Calculate Real GNP

Use base year prices × current year quantities for everything. This shows what the same output would have cost if prices hadn't changed.

Step 3: Apply the formula

If Nominal GNP = ₹120 lakh crore and Real GNP = ₹100 lakh crore, then:

This means the general price level has risen by 20% since the base year.

Why It Matters (and Where It Differs from CPI)

The GNP Deflator serves three critical purposes in macroeconomics:

1. Converting nominal to real values — If you know the deflator, you can "deflate" any nominal GNP figure to find real GNP:

2. Measuring economy-wide inflation — The percentage change in the GNP Deflator from one year to the next gives the inflation rate for all domestically produced goods and services.

3. Comparing across time — Without the deflator, comparing India's GNP in 1990 to 2024 would be meaningless because prices have changed so much.

The Key Insight NCERT Expects You to Know …