NCERT Solutions Curiosity Chapter 4 Activity 4.6: Let us investigate (demonstration activity) — Effect of Air and Water on Other Metals
Book page 51 Updated on2026-09-05
Q1.
Let the magnesium ribbon burn. What do you observe?
Answer
The magnesium ribbon burns with a dazzling white flame and changes into a white powder. Collect the powder on a watch glass.
Magnesium + oxygen (of the air) on burning → magnesium oxide Silvery ribbon → blinding white light → white powder
Why it happens: magnesium reacts with the oxygen present in the air. So much energy is released that the light is painfully bright, and the new substance formed — magnesium oxide — is a white powder quite unlike the shiny grey ribbon you started with.
Caution: this is a demonstration activity, done by the teacher. Wear protective eyeglasses, keep a safe distance and never look straight at the flame — the light can hurt the eyes. Clean the ribbon with sandpaper first, and hold it with a pair of tongs.
Q2.
Recall the chapter ‘Exploring Substances: Acidic, Basic, and Neutral’. Find out whether the solution of magnesium oxide is acidic or basic or neutral in nature. You can use any acid-base indicator.
Answer
Add a few drops of warm water to the white powder, stir it well and test the solution. It is basic.
Indicator used
What you see
What it means
Red litmus paper
Turns blue
Basic
Blue litmus paper
Stays blue (no change)
Not acidic
Turmeric (haldi) paper
Turns reddish-brown
Basic
China rose indicator
Turns green
Basic
Generally, oxides of metals are basic in nature.
Tip: use warm water — magnesium oxide dissolves very little in cold water, and a weak solution may not change the indicator clearly.
Q3.
What effect does this solution have on blue and red litmus papers?
Answer
Red litmus paper → turns blue
Blue litmus paper → no change, stays blue Therefore the solution of magnesium oxide is basic in nature.
Dip both papers, not just one. A substance is proved basic only when the red one turns blue and the blue one is unchanged.
Why it matters: this one test result stands for a whole family. Magnesium is a metal, its oxide dissolves to give a basic solution, and the same is true for metals in general — metal oxides are basic. You will meet this burning of magnesium again in the chapter ‘Changes Around Us: Physical and Chemical’.