Questions

Given Equation is 

Mg + O2 → MgO

Balancing the Chemical Equation is nothing but Conservation of Matter. As Matter is Neither created nor Destroyed, it must be conserved.

Here we have 1 Mg and 2 O on the left side and 1 Mg and 1 O on the right side

To balance that, add 1 Mg on the left side so that it becomes 2 Mg and 2 O on the left side

i.e,

2 Mg + O2 → 2 MgO

Here it has 2 Mg & 2 O on the left side and 2 Mg and 2 O on the right side and the Chemical equation is Balanced.

A) Cooking of Food  ------ Chemical Change

B) Digestion of Food ----- Chemical Change

C) Freezing of water ----- Physical Change

D) Water is heated up ---- Physical Change

because here the chemical composition of the substance changes in A & B only.

Since we know that, If the chemical composition is changing then it is a chemical change and if the chemical composition is remaining the same, then it is a physical change.

The Central Excise Day (CED) is celebrated every year on February 23 in India to commemorate the enactment of the Central Excise and Salt Act, 1944. The Central Excise officers all over the country celebrate this day by organizing seminars, workshops, trade interactions and cultural events etc.

The relative pronoun acts as the subject or object of the relative clause. It replaces words like she, he, him, her, they, them etc.

It is, therefore, wrong to repeat the pronoun in the relative clause.

Hence, the correct sentence is Shreya, who is my best friend, is a singer.