Which one of the following metals produces hydrogen with cold water?
- A.Silver
- B.Sodium
- C.Copper
- D.Iron
Correct answer
Explanation
The correct answer is B, Sodium. Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas: 2Na + 2H₂O → 2NaOH + H₂.
Sodium is an alkali metal near the top of the reactivity series. The reaction gives out so much heat that the hydrogen released often catches fire, which is why sodium and potassium are stored under kerosene, away from air and moisture. Calcium also reacts with cold water, but less violently, and the hydrogen bubbles stick to it and make it float. Magnesium reacts only with hot water, while metals like aluminium, zinc and iron react only with steam. Metals below hydrogen in the series do not give hydrogen with water at all.
A is wrong: silver is a noble metal that does not react with water.
C is wrong: copper does not react with water, even steam.
D is wrong: iron reacts only with steam, forming iron oxide and hydrogen.
Exam tip: Cold water — Na, K, Ca; hot water — Mg; steam — Al, Zn, Fe; no reaction — Cu, Ag, Au.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →