What is so fragile that saying its name breaks it?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

The first two letters signify a male, the first three letters signify a female, the first four letters signify a great, while the entire world signifies a great woman. What is the word?

Can you solve the below algebraic mathematical equation?

(J+O+I+N+T)3 = JOINT

I welcome the day with a show of light, I stealthily came here in the night. I bathe the earthy stuff at dawn, But by noon, alas! I'm gone.

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

In the city of Brain Teasers, 5% of people do not list their phone numbers. Now if we select random 100 people from the phone directory, then how many people selected will have unlisted phone numbers?

In a jungle where there are no street lights or any other artificial source of lights, I notice a black snake crossing the road.
How did I get sight of the snake?