Science Class 7th

261. The representation of a molecule of a compound in the form of symbol is called _________

A) Chemical reaction

B) Molecular formula

C) Ionic bond

D) Chemical formula

262. Atoms of same elements having same number of protons but different number of neutrons are called _______

A) Isotone

B) Isotope

C) Molecule

D) Mole

263. Protium is called _________

A) Ordinary hydrogen

B) Heavy hydrogen

C) Radioactive hydrogen

D) None of these

264. Deuterium is called ____

A) Ordinary hydrogen

B) Heavy hydrogen

C) Radioactive hydrogen

D) None of these

265. Tritium is called _______

A) Ordinary hydrogen

B) Heavy hydrogen

C) Radioactive hydrogen

D) None of these

266. Naturally occurring hydrogen contains the largest percentage of _________

A) Protium

B) Deuterium

C) Tritium

D) None of these

267. _________has one proton, no neutron, and one electron.

A) Protium

B) Deuterium

C) Tritium

D) None of these

268. The percentage of deuterium In naturally occurring hydrogen is about _______

A) 0.0051%

B)   0.0015%

C)   0.00015%

D)   0.00051%

269. ________has one proton, one neutron, one electron.

A) Protium

B) Deuterium

C) Tritium

D) None of these

270. The number of tritium isotope is one in_______ millions.

A) Twenty

B) Eight

C) Ten

D) Five

271. _______has one proton, two neutrons and one electron.

A) Tritium

B) Protium

C) Deuterium

D) None of these

272. Atoms of different elements with different atomic number but have same mass number are called _______

A) Isotope

B) Isobars

C) Isotone

D) None of these

273. 71. Water contain ________ hydrogen.

A) 10%

B)   15%

C)   11%

D)   11.11%

274. Water contain ____ Oxygen.

A) 88.88%

B)   88%

C)   90%

D)   92%

 

275. An atom of carbon contains 6 protons and 6 neutrons, its mass number will be_______.

A) 12

B) 6

C) 18

D) 24

276. An element has seven electrons in its valence shell. its Valency is ________

A) 7

B) 0

C) 1

D) 8

277. A _________is a property that is measurable and whose value describes a state of a physical system.

 A) Chemical property

B) Physical property

C) Reversible property

D) Irreversible property

 

278. The property where chemical composition or identity of the substance is changes is called ______

A) Physical property

B) Chemical property

C) Option A is correct

D) None of these

279. The changes that can be reversed are called _________

A) Irreversible change

B) Chemical change

C) Reversible change

D) None of these

280. Melting of ice is

A) Irreversible change

B) Chemical change

C) Reversible change

D) None of these