Questions

We know that polar substances are soluble in polar solvents and non polar substances are soluble in non-polar solvents only. Here the hydrocarbons are non-polar molecular substances and water is a polar solvent. So water can't dissolve hydrocabons.

Hence, as hydrocarbons are non-polar substances, they are insoluble in water as it is a highly polar solvent. 

Magnesium is dissolved in seawater at a concentration of about 1,000 parts per million and is the only metal directly extracted from seawater.

In the above given sentences, only option C) The hen has laid 10 eggs is gramatically correct.

A) Not correct - We had gone to the party last night

Correct - We went to the party last night

B) Not correct - I have seen him yesterday

Correct - I saw him yesterday (We do not use the present perfect tense with past time expressions.)

D) Not correct - She is sleeping for 2 hours

Correct - She has been sleeping for two hours. (We use the present perfect continuous tense to show duration.)

DNA is a very long chain polymer made up of thousands of repeating units called nucleotides.

Nucleotide Unit is composed of a phosphate group, a pentose sugar, and a nitrogenous base.

The sides of the DNA ladder are made up of alternating deoxyribose sugar -- phosphate group units.

RST 6.5 & RST 5.5 are level-triggering interrupts.